how to 
by randall munroe 




RIVERHEAD BOOKS
An imprint of Penguin Random House LLC
Copyright © 2019 by xkcd inc.
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ISBN 9780525537090 (hardcover)
ISBN 9780525537106 (ebook)
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Version_1
Contents
Title Page
Copyright
Disclaimer
Introduction
1. How to Jump Really High
2. How to Throw a Pool Party
3. How to Dig a Hole
4. How to Play the Piano
→ How to Listen to Music
5. How to Make an Emergency Landing
6. How to Cross a River
7. How to Move
8. How to Keep Your House from Moving
→ How to Chase a Tornado
9. How to Build a Lava Moat
10. How to Throw Things
11. How to Play Football
12. How to Predict the Weather
→ How to Go Places
13. How to Play Tag
14. How to Ski
15. How to Mail a Package
16. How to Power Your House (on Earth)
17. How to Power Your House (on Mars)
18. How to Make Friends
→ How to Blow out Birthday Candles
→ How to Walk a Dog
19. How to Send a File
20. How to Charge Your Phone
21. How to Take a Selfie
22. How to Catch a Drone
23. How to Tell If You’re a Nineties Kid
24. How to Win an Election
25. How to Decorate a Tree
→ How to Build a Highway
26. How to Get Somewhere Fast
27. How to Be On Time
28. How to Dispose of This Book
Acknowledgements
References
Index
→ How to Change a Light Bulb
About the Author
Disclaimer
Do not try any of this at home. The author of this book is an internet cartoonist,
not a health or safety expert. He likes it when things catch fire or explode, which
means he does not have your best interests in mind. The publisher and the author
disclaim responsibility for any adverse effects resulting, directly or indirectly,
from information contained in this book.
Hello!
This is a book of bad ideas.
At least, most of them are bad ideas. It’s possible some good ones slipped
through the cracks. If so, I apologize.
Some ideas that sound ridiculous turn out to be revolutionary. Smearing mold
on an infected cut sounds like a terrible idea, but the discovery of penicillin
showed that it could be a miracle cure. On the other hand, the world is full of
disgusting stuff that you could smear on a wound, and most of them won’t make
it better. Not all ridiculous ideas are good. So how do we tell the good ideas
from the bad?
We can try them and see what happens. But sometimes, we can use math,
research, and things we already know to work out what will happen if we do.
When NASA was planning to send its car-size Curiosity rover to Mars, they
had to figure out how to land it gently on the surface. Previous rovers had landed
using parachutes and air bags, so NASA engineers considered this approach with
Curiosity, but the rover was too large and heavy for parachutes to slow it down
enough in Mars’s thin atmosphere. They also thought about mounting rockets on
the rover to let it hover and touch down gently, but the exhaust would create dust
clouds that would obscure the surface and make it hard to land safely.
Eventually, they came up with the idea of a “sky crane”—a vehicle that would
hover high above the surface using rockets while lowering Curiosity to the
ground on a long tether. This sounded like a ridiculous idea, but every other idea
they could come up with was worse. The more they looked at the sky crane idea,
the more plausible it seemed. So they tried it, and it worked.
We all start out life not knowing how to do things. If we’re lucky, when we
need to do something, we can find someone to show us how. But sometimes, we
have to come up with a way to do it ourselves. This means thinking of ideas and
then trying to decide whether they’re good or not.
This book explores unusual approaches to common tasks, and looks at what
would happen to you if you tried them. Figuring out why they would or wouldn’t
work can be fun and informative and sometimes lead you to surprising places.
Maybe an idea is bad, but figuring out exactly why it’s a bad idea can teach you
a lot—and might help you think of a better approach.
And even if you already know the right way to do all these things, it can be
helpful to try to look at the world through the eyes of someone who doesn’t.
After all, for anything that “everyone knows” by the time they reach adulthood,
every day over 10,000 people in the United States alone are learning it for the
first time.
That’s why I don’t like making fun of people for admitting they don’t know
something or never learned how to do something. Because if you do that, all it
does is teach them not to tell you when they’re learning something . . . and you
miss out on the fun.
This book may not teach you how to throw a ball, how to ski, or how to move.
But I hope you learn something from it. If you do, you’re one of today’s lucky
10,000.

CHAPTER 1
How to Jump Really High
People can’t jump very high.
Basketball players make some impressive leaps to reach hoops placed high in
the air, but most of their reach comes from their height. An average professional
basketball player can only jump a little more than 2 feet straight up. Non-athletes
are more likely limited to jumping a foot or so. If you want to jump higher than
that, you’ll need some help.
Using a running start can help. This is what athletes competing in the high
jump do, and the world record height is 8 feet. However, that’s measured from
the ground. Since high jumpers tend to be tall, their center of mass starts off
several feet off the ground, and because of how they fold their bodies to pass
over the bar, their center of mass may actually pass under it. An 8-foot high
jump doesn’t involve launching the center of their body anything like the full 8
feet.
If you want to beat a high jumper, you have two options:
1. Dedicate your life to athletic training, from an early age, until you
become the world’s best high jumper.
2. Cheat.
The first option is no doubt an admirable one, but if that’s your choice, then
you’re reading the wrong book. Let’s talk about option two.
There are a lot of ways you could cheat at high jump. You could use a ladder
to get over the bar, but that’s hardly jumping. You could try wearing those
spring-loaded stilts* popular with extreme sports enthusiasts, which—if you’re
athletic enough—might be enough to give you the edge over an unassisted high
jumper. But for sheer vertical height, athletes have already come up with a better
technique: pole vaulting.
In pole vaulting, athletes start running, stick a flexible pole into the ground in
front of them, and launch themselves into the air. Pole vaulters can fling
themselves several times higher than the best unassisted high jumpers.
The physics of pole vaulting are interesting, and don’t revolve around the pole
nearly as much as you might think. The key to vaulting isn’t the springiness of
the pole, it’s the athlete’s running speed. The pole is just an efficient way to
redirect that speed upward. In theory, the vaulter could use some other method to
change direction from forward to up. Instead of sticking a pole in the ground,
they could jump onto a skateboard, go up a smooth curved ramp, and reach just
about exactly the same height as the vaulter.
We can estimate a pole vaulter’s maximum height using simple physics. A
champion sprinter can run 100 meters in 10 seconds. If an object is launched
upward at that speed under Earth’s gravity, a little math can tell us how high it
should go:
Since the pole vaulter is running before they jump, their center of gravity
starts off above the ground already, which adds to the final height it reaches. A
normal adult’s center of gravity is somewhere in their abdomen, usually at a
height of about 55 percent of their actual height. Renaud Lavillenie, the world
record holder in the men’s pole vault, is 1.77 meters tall, so his center of gravity
adds another 0.97 meters or so, giving a final predicted height of 6.08 meters.
How does our prediction compare to reality? Well, the actual world record
height is 6.16 meters. That’s pretty close for a quick approximation!*
Of course, if you show up at a high jump championship with a vaulting pole,
you’ll be immediately disqualified.* But while the judges might object, they
probably won’t stop you, especially if you wave the pole around threateningly as
you approach.
Your record won’t go on the books, but that’s ok—you’ll know in your heart
how high you jumped.
But if you’re willing to cheat more blatantly, you can go higher than 6 meters.
A lot higher. You just need to find the right spot to launch from.
Runners take advantage of aerodynamics. They wear sleek, tight-fitting outfits
to cut down on air resistance, which helps them to gain greater speeds and thus
soar higher.* Why not take it a step further?
Of course, actually pushing yourself forward with a propeller or a rocket
doesn’t count. There’s no way you can call that a “jump” with a straight face.*
That’s not a jump, that’s a flight. But there’s nothing wrong with just . . . gliding
a little.
The path of every falling object is affected by how the air moves around it.
Ski jumpers adjust their shape to gain a huge aerodynamic boost to their jumps.
In an area with the right winds, you can do the same thing.
When sprinters run with the wind at their backs, they can reach higher speeds.
Similarly, if you jump in an area where the wind is blowing upward, you can
reach greater heights.
It takes strong wind to push you upward—wind blowing faster than your
terminal velocity. Your terminal velocity is the maximum speed you’ll reach
while falling through air, when the force of the air rushing past balances out the
downward acceleration of gravity. This is the same as the minimum upward
wind speed needed to lift you off the ground. Since all motion is relative, it
doesn’t really matter whether you’re falling downward through the air or the air
is blowing upward past you.*
People are a lot denser than air, so our terminal velocity is pretty high. A
falling person’s terminal velocity is around 130 miles per hour (mph). In order to
get much of a boost from wind, you’ll need the upward wind speed to be at least
in the same range as your terminal velocity. If the wind is a lot slower, then it
won’t affect your jump height very much.
Birds use columns of warm, rising air—called thermals—like elevators. The
birds soar in circles without flapping, letting the rising air carry them upward.
These thermal updrafts are relatively weak; to lift your larger human body,
you’ll need to find a stronger source of rising air.
Some of the strongest updrafts near the ground happen near mountain ridges.
When wind encounters a mountain or ridge, the airflow can be diverted upward.
In some areas, these winds can be quite fast.
Unfortunately, even at the best spots, the vertical winds generally aren’t even
close to a human’s terminal velocity. At best, you’d only gain a little bit of
height from the wind’s assist.*
Instead of trying to increase the wind speed, you can try reducing your
terminal velocity with aerodynamic clothing. A good wingsuit—clothing with
sheets of material between the arms and legs—can reduce a person’s sink rate
from 130 mph to as little as 30 mph. That’s still not enough to actually ride
winds upward, but it would add some height to your jump. On the other hand,
you’d have to do your running approach in a full wingsuit, which would
probably cancel out the benefit from the wind.
To add substantial height to your jump, you need to go beyond wingsuits, into
the world of parachutes and paragliders. These large contraptions reduce a
person’s falling speed enough so that surface winds can easily get strong enough
to lift them. Skilled paragliders can launch from the ground and ride ridge winds
and thermals to thousands of feet.
But if you want a real high jump record, you can do even better.
In most areas where air flows over mountains, the “mountain waves” extend
up only into the lower atmosphere, which limits the height that gliders can reach.
But in some places, when conditions are just right, these disturbances may
interact with the polar vortex and polar night jet,* creating waves that reach into
the stratosphere.
In 2006, glider pilots Steve Fossett and Einar Enevoldson rode stratospheric
mountain waves to over 50,000 feet above sea level. That’s almost twice as high
as Mt. Everest, and higher than the highest commercial airline flights. That flight
set a new glider altitude record. Fossett and Enevoldson say they could have
ridden the stratospheric waves even higher—they only turned back because the
low air pressure caused their pressure suits to inflate so much that they couldn’t
operate the controls.
If you want to jump high, you just need to construct an outfit shaped like a
sailplane—you can make one out of fiberglass resin and carbon fiber—and head
to the mountains of Argentina.

If you find the right spot, and if conditions are just right, you can seal yourself
into your sailplane suit,* jump into the air, catch the ridge lift, and ride the wind
into the stratosphere. It’s possible that a glider pilot riding these waves might be
able to cruise at higher altitudes than any other wing-borne aircraft. That’s not
bad for a single jump!*
If you’re really lucky, maybe you can find a spot that’s upwind from where
the Olympics are being held. That way, when you jump off the edge, the winds
in the stratosphere will carry you over the venue . . .
. . . letting you set the greatest high jump record in the history of the sport.
They probably won’t give you a medal, but that’s fine. You’ll know you’re
the real champion.
CHAPTER 2
How to Throw a Pool Party
You’ve decided to throw a pool party. You’ve got everything—snacks, drinks,
floating inflatable toys, towels, and those rings you throw into the pool and then
have to dive in to retrieve. But the night before the party, you can’t shake the
feeling that you’re missing something. Looking around your yard, you realize
what it is.
You don’t have a pool.
Don’t panic. You can solve this problem. You just need a bunch of water and
a container to put it in. Let’s figure out the container first.
There are two main types of pools: in-ground and above-ground.
IN-GROUND POOL
An in-ground pool is, when it comes down to it, a fancy hole. This type of pool
can take more work to install, but is also less likely to collapse in the middle of
your party.
If you’d like to build an in-ground pool, first consult chapter 3: How to Dig a
Hole. Use those instructions to dig a hole roughly 20 feet by 30 feet by 5 feet.
Once you’ve created a hole of the appropriate size, you may want to line the
walls with some kind of coating to keep the water from turning to mud or
draining out before the party is over. If you have some giant plastic sheets or
tarps lying around, you can use those, or you can try a spray-on rubber coating—
there are ones designed for lining the beds of koi ponds. Just tell the salespeople
you have some really large koi.

ALTERNATIVE: ABOVE-GROUND POOL
If you decide an in-ground pool isn’t the option for you, you can instead try an
above-ground pool. The design of this type of pool is relatively simple:
Unfortunately, water is heavy—ask anyone who’s ever filled a fish tank on
the floor and then tried to lift it up onto a table. Gravity pulls the water
downward, but the ground pushes back equally hard. The water pressure is
redirected outward, toward the walls of the pool, which are stretched in all
directions. This tension, called hoop stress, is strongest at the base of the wall
where the water pressure is the highest. If the hoop stress exceeds the tensile
strength of the wall, the wall will burst.*
Let’s pick a possible material—say, aluminum foil. How deep can the water in
an aluminum-foil-walled pool get before the sides burst? We can figure out the
answer to this question, and lots of other pool design questions, using the
formula for hoop stress:
Let’s plug in the numbers for aluminum foil. Aluminum has a tensile strength
of around 300 megapascals (MPa), and sheets of foil are roughly 0.02 mm thick.
Let’s assume our pool is 30 feet in diameter, so there’s plenty of room for
games. We can plug those values into the hoop stress equation and rearrange
things to figure out how deep the water in our shiny, crinkly pool can get before
the hoop stress equals the tensile strength of the aluminum and the walls give
out:
Sadly, 5 inches of water is probably not enough for a pool party.
If we swap out the thin aluminum foil for inch-thick pieces of wood, the math
looks much better. Wood has a lower tensile strength than aluminum foil, but it
makes up for it by being thicker, and could hold water 75 feet deep. If you
happen to have a 30-foot-wide wooden cylinder with inch-thick walls lying
around, that’s great news for you!
You can also rearrange the equation to tell you how thick the pool’s walls
need to be to support a desired water depth. Let’s say we want our pool to be
about 3 feet deep. Given the tensile strength of a material, this version of the
formula tells us the minimum wall thickness necessary to hold the water:
The great thing about physics is that you can run these numbers for any
material you want, even if it’s something ridiculous. Physics doesn’t care if your
question is weird. It just gives you the answer, without judging. For example,
according to the comprehensive 456-page handbook Cheese Rheology and
Texture, hard Gruyere cheese has a tensile strength of 70 kPa. Let’s plug that
into the formula!
Good news! You’ll only need a two-foot-thick wall of cheese to contain your
pool! The bad news is that you may have trouble convincing anyone to jump in.
Given the practical problems associated with cheese, you should probably
stick to traditional materials like plastic and fiberglass. Fiberglass has a tensile
strength around 150 MPa, which means a wall just a millimeter thick would be
strong enough to contain the water with extra tensile strength to spare.
GET SOME WATER
Now that you’ve got your pool—whether in-ground or above-ground—you’ll
need some water. But how much?
Standard backyard in-ground pools vary in size, but a medium-size one large
enough to have a diving board might hold 20,000 gallons of water.
If you have a garden hose and a municipal water supply, then you could
potentially fill your pool that way. But whether or not you can fill a pool quickly
depends on the flow rate from your hose.
If you have good water pressure and a large-diameter hose, your flow rate
might be 10 or 20 gallons per minute, which is enough to fill your pool within a
day or so. If your flow rate is too low—or if you have well water, which may run
out before you fill your pool—you might need to look for a different solution.

INTERNET WATER
In many areas, online retailers like Amazon offer same-day delivery. A 24-pack
of Fiji water bottles currently costs about $25. If you have $150,000 to spare—
plus another $100,000 or so for same-day delivery—you can simply order a pool
in bottle form. As a bonus, your new pool will consist entirely of water shipped
from Fiji.
This will present a new challenge. When the water is delivered, you’ll need to
get it all into the pool.
This will be trickier than you might have thought. Sure, you could unscrew
the cap on each bottle and dump the water into the pool one by one, but this
would take a few seconds per bottle. Since there are 150,000 bottles and only
86,400 seconds in a day, anything that takes more than a second per bottle is
definitely not going to work.
ATTACK THE BOTTLES
You could try slicing the caps off an entire 24-pack of bottles with a sword.
Many slow-motion videos online show people cutting through a row of water
bottles with a sword. Judging from the videos, it’s surprisingly hard to do—the
sword tends to be deflected up or down as it passes through the bottles. Even if
you had a precise enough swing, along with the requisite arm strength and
endurance, using a sword would probably be too slow.
Guns probably wouldn’t work too well, either. With careful planning and an
efficient setup, you could use some kind of shotgun to make holes in a whole
case of bottles at once, but you’d still have a hard time puncturing all the bottles
and making them all fully drain fast enough to get through them all. You’d also
end up with a pool full of lead, which—especially if you added chlorine to the
water—would corrode and could eventually contaminate the groundwater.
There are a wide variety of increasingly powerful weapons you could use to
try to open these bottles quickly; we won’t run through them all here. But before
we leave weapons behind and move on to a more practical solution, let’s take a
moment to consider the biggest and most impractical option of all. Could you
open bottles using nuclear bombs?
This is a completely ridiculous suggestion, so it should come as no surprise
that it was studied by the US government during the Cold War. Early in 1955,
the Federal Civil Defense Administration bought beer, soda, and carbonated
water from local stores, then tested nuclear weapons on them.*
Now, they weren’t trying to open the beverages. The purpose of the test was
to see how well the containers survived, and whether the contents were
contaminated. The civil defense planners figured that, after a nuclear explosion
in a US city, potable water would likely be needed by first responders, and they
wanted to know whether commercial beverages would be a safe source of
hydration.*
The saga of the government’s nuclear war on beer is cataloged in a 17-page
report titled The Effect of Nuclear Explosions on Commercially Packaged
Beverages, a copy of which was helpfully unearthed by nuclear historian Alex
Wellerstein.
The report describes how the bottles and cans were placed in various locations
around the Nevada test site for each explosion. Some were in refrigerators, some
on shelves, and some just sitting on the ground.* They carried out the
experiment twice, during two different nuclear tests conducted as part of
Operation Teapot.
The beverages fared surprisingly well. Most of them survived the blast intact.
Those that didn’t were mostly punctured by flying debris or exploded when
knocked off the shelves. They also had low levels of radioactive contamination,
and even tasted ok.
Post-explosion beer samples were sent for “carefully controlled testing” at
“five qualified laboratories.”* The consensus was that the beer mostly tasted
fine. They concluded that beer recovered after a nuclear blast could be
considered a safe source of emergency hydration, but that it should probably be
tested more carefully before it was put back on the market.
Plastic bottles weren’t common in the 1950s, so all the tests used glass and
metal bottles. However, the tests still suggest that nuclear weapons probably
don’t make great bottle openers.
INDUSTRIAL SHREDDERS
Luckily for us, there’s a type of device which can accomplish our goal much
more quickly than a sword, shotgun, or nuclear weapon: an industrial plastic
shredder. Shredders are used by recycling centers to shred large volumes of
plastic bottles, and—as a bonus—they can strain out the liquid for you.
A shredder like the Brentwood AZ15WL 15kW can handle a throughput of 30
tons per hour—including both plastic and liquid, according to Brentwood
marketing materials. This would let you fill your pool in a little over 2 hours.
Industrial shredders come with price tags in the five to six figures, which is a
lot for one party (although it’s nothing compared to what you already spent on
water bottles.) But maybe, if you mention how many nuclear weapons you have,
you can convince them to give you a discount.
LET SOMEONE ELSE DO THE WORK
If someone else has a pool nearby, and they’re at a slightly higher elevation, you
can steal the water using a siphon. If you can connect the two pools with a tube
of water, you can get water to flow steadily from their pool into yours.
Note: Siphons can lift water up out of a pool and over small barriers like
fences, but if the middle of the siphon goes more than 30 feet above the surface
of your neighbor’s pool, water won’t flow. Siphons are driven by atmospheric
pressure, and Earth’s air pressure is only capable of pushing water up 30 feet
against gravity.
GET WATER BY MAKING IT
Water is made up of hydrogen and oxygen. There’s plenty of oxygen in the
atmosphere,* and while hydrogen is certainly rarer, it’s still not too hard to find.
The good news is that if you get a bunch of hydrogen and oxygen together,
it’s easy to turn it into water. You just apply a little bit of heat, and the chemical
reaction keeps going. In fact, it’s pretty hard to stop.
The bad news is that sometimes the chemical reaction gets started by accident.
We used to have big hydrogen-filled airships flying around, but after some
dramatic incidents in the 1930s, we started filling them with helium instead.
Nowadays, if you want hydrogen, the best place to get it is by collecting and
reprocessing the byproduct of fossil fuel extraction.
GET WATER FROM THE AIR
You don’t need to combine hydrogen and oxygen to create water when there’s
already-created H2O floating around in the air in the form of water vapor—the
stuff that condenses to form clouds and sometimes even falls in the form of rain.
On average, each square meter of the Earth has about 6 gallons of water in the
column of air above it, the equivalent of a couple of 24-packs of water bottles.*

If all that water fell as rain, it would form a layer about an inch thick. If your
property is 1 acre in size, and the air has an average amount of moisture, then
there are about 25,000 gallons of water in the air overhead. That’s enough to fill
a pool! Unfortunately, a lot of that water is pretty high up and hard to get to. It
would be nice if we could make the water fall on cue, but despite periodic
attempted cloud-seeding projects, no one has found a way to reliably induce
rainfall.

The usual way of extracting water from air is to make the air flow past a cold
surface, so the water condenses out of it as dew. To get all the water out of your
air, you’d need to build a several-mile-high cooling tower. Luckily for you, air
moves around on its own, so you don’t need to build a mile-high tower—if
there’s a breeze, you can just collect the moisture from the air as it flows past
your house.
Moisture collection is really a pretty inefficient way to gather water. It takes a
lot of power to cool and condense water out of the air. In most cases, you’d use a
lot less energy by just driving a truck to an area with more water, filling it up,
and driving back. Besides, even under ideal conditions, this kind of humidifier is
unlikely to produce enough water to fill your pool any time soon, and it might
annoy your neighbors who live downwind of you.
GET WATER FROM THE SEA
There’s a lot of water in the sea,* so probably no one will mind if you borrow a
little. If your pool is below sea level, and you don’t mind a saltwater pool, this
might be an option. All you need to do is dig a channel and let the sea flow in.
This has actually happened in real life, by accident, very dramatically.
Malaysia was once the world’s largest producer of tin. One of the mines that
produced this tin was constructed near the western coast, just a few hundred feet
from the ocean. After the tin market collapsed in the 1980s, the mine was
abandoned. On October 21, 1993, the water broke through the narrow barrier
separating the mine from the sea. The ocean rushed in, filling the mine in a
matter of minutes. The lagoon created by the flood remains to this day, and can
be seen on maps at 4.40°N, 100.59°E. The cataclysm was recorded by a
bystander with a camcorder, and the footage has since been uploaded to the
internet. Despite its low quality, it’s one of the most jaw-dropping pieces of
video ever recorded.*
If the bottom of your pool is above sea level, connecting it to the ocean won’t
work; water would just flow downhill to the sea. But what if you could bring the
sea up to you?
Well, you’re in luck; it’s happening whether you want it to or not. Thanks to
the trapped heat caused by greenhouse gases, the seas have been rising for many
decades now. Sea-level-rise is caused by a combination of melting ice and
thermal expansion of the water. If you want to fill your pool, you could try
accelerating sea-level rise. Sure, it would worsen the immeasurable ecological
and human toll of climate change, but on the other hand, you could have a sweet
pool party.
If you wanted to cause rapid sea-level-rise, and you happened to have a giant
ice sheet on the land next to your house, you might think that melting it would
be a great way to raise the sea level.
But, because of some counterintuitive physics, melting an ice sheet next to
your house might actually lower the sea level. What you want to do is melt ice
on the other side of the world.
The reason for this bizarre effect is gravity. Ice is heavy, and when it’s sitting
on land, it pulls the ocean slightly toward it. When it melts, the water level goes
up on average, but since it’s no longer being pulled as hard toward the land, it
can actually go down in the area around the ice that melted.
When ice from the Antarctic ice cap melts, sea level goes up the most in the
northern hemisphere. When ice in Greenland melts, on the other hand, it raises
sea levels most around Australia and New Zealand. If you want to raise sea level
near where you live, check whether there’s an ice sheet on the other side of the
planet. If so, that’s the one you should melt.
GET WATER FROM THE LAND
If there are no convenient ice caps to melt—or you don’t want to contribute to
global sea-level-rise—you could try to do what farmers have been doing to get
water for thousands of years: borrow a river.
You could find a nearby river and encourage it—via a temporary dam—to
flow toward your pool long enough to fill it up. But be careful: this kind of
project has gone wrong before.
In 1905, engineers on the California/Arizona border were digging irrigation
canals to bring water to farms from the Colorado River. The mission to divert
water from the Colorado River was, unfortunately, too successful. The water
flowing into the new canal started eroding a deeper and wider path, which let
more water flow in. Before they could pull the plug,* the river had been captured
completely. It inundated a formerly dry valley downstream from the irrigation
project, filling it and creating a new—completely accidental—inland sea.
The Salton Sea, which has waxed and waned over the last century, is currently
drying up as more water is diverted for irrigation. The windblown dust from the
dry lake bed, contaminated with agricultural runoff and other pollutants, blows
through nearby towns, sometimes making it hard to breathe. The contaminated,
increasingly salty water has led to massive die-offs of aquatic life, and the
decaying algae and dead fish have created an omnipresent rotten-egg smell
which occasionally wafts west as far as Los Angeles.
That might sound bad, but don’t worry—those disastrous environmental
consequences took a while to develop.
In fact, the Salton Sea was briefly popular as a resort destination, with yacht
clubs, fancy hotels, and swimming. Later, as conditions in the sea deteriorated,
the resorts all turned to ghost towns. But you can worry about all those
consequences tomorrow.
For now, it’s pool party time!
CHAPTER 3
How to Dig a Hole
There are lots of reasons to dig holes. You might be planting a tree, installing an
in-ground pool, or putting in a driveway. Or perhaps you’ve found a treasure
map, and you’re digging at the X.
The best way to dig a hole depends on the size of the hole you want to create.
The simplest digging tool is a shovel.
DIGGING WITH A SHOVEL
The rate at which you can dig using a shovel will depend on what kind of dirt
you’re trying to excavate, but a person digging with a shovel can typically
remove between 0.3 and 1.0 cubic meters of dirt per hour. At those rates, in 12
hours, you might be able to excavate a hole about this large:
But if you’re digging a hole to get at buried treasure, at some point you may
want to stop to consider the economics of the situation.
Digging holes is labor, and labor is valuable. According to the Bureau of
Labor Statistics, construction laborers earn an average of $18 per hour. The rate
a contractor might charge for an excavation project would also include the cost
of planning, equipment, transportation to and from the work site, and disposal of
any waste, and likely works out to an hourly rate several times higher. If you
spend 10 hours digging a hole in order to find treasure worth $50, you’re
working for far below minimum wage. In principle, you’d be better off just
getting a job digging up driveways somewhere, and in the end, you’d make more
money than you would from the treasure.
You also might want to double-check the authenticity of your pirate treasure
map, because pirates didn’t actually bury treasure.
That’s not quite true. There was one time that a pirate buried treasure
somewhere. One time. And the entire idea of buried pirate treasure comes from
that one incident.
BURIED PIRATE TREASURE
In 1699, Scottish privateer* William Kidd was about to be arrested for various
maritime crimes.* Before sailing to Boston to confront the authorities, he buried
some gold and silver on Gardiners Island, off the tip of Long Island in New
York, for safekeeping. It wasn’t exactly a secret—he buried it with the
permission of the island’s proprietor, John Gardiner, along a pathway west of the
manor house. Kidd was arrested and eventually executed, and the island’s
proprietor handed the treasure over to the Crown.
Believe it or not, that’s the entire history of buried pirate treasure. The reason
“buried treasure” is such a well-known trope is that Captain Kidd’s story helped
inspire Robert Louis Stevenson’s novel Treasure Island, which almost singlehandedly* created the modern image of the pirate.
In other words, this is the only pirate treasure map that has ever existed, and
the treasure is gone now:
The scarcity of actual buried pirate treasure hasn’t stopped people from
searching. After all, just because pirates didn’t bury treasure doesn’t mean
there’s never anything valuable in the ground. People who dig a lot of holes,
from treasure hunters to archaeologists to construction workers, certainly find
valuable stuff from time to time.
But perhaps there’s also something compelling about the act of digging for
treasure itself—because sometimes people seem to go a little overboard.
OAK ISLAND MONEY PIT
Since at least the mid-1800s, people have believed there’s buried treasure near a
particular spot on Oak Island in Nova Scotia. Successive groups of treasure
hunters have dug deeper and deeper holes in attempts to unearth the treasure.
The actual origin of the stories is murky, but at this point it’s become almost a
meta-myth: most of the evidence that something mysterious is buried on Oak
Island consists of stories about evidence that may or may not have been found
by previous searchers.
No treasure has been found. Even if a large chest of gold had been buried on
the island, the value of the aggregate time and effort that successive generations
of treasure hunters have invested in searching for it would by now almost
certainly exceed the value of the treasure.
So how big a hole is it worth digging to recover different kinds of treasure?
A single gold doubloon—the classic pirate treasure—is currently*
,* worth
about $300. If you know where a doubloon is buried, it’s not worth it to hire
someone to dig it out unless the job costs less than $300. And if you value your
own labor at $20/hour, then you shouldn’t spend more than 15 hours digging it
up.
On the other hand, if the treasure is a chest of gold, it could be worth a lot
more than $300. A single 1-kilogram gold bar is worth about $40,000, so a chest
containing 25 gold bars is worth about a million dollars. If the hole you need to
dig is more than 20,000 cubic meters—equivalent to a 30 m × 30 m × 20 m hole
—then it will take you so long to dig that the value of the labor involved in the
digging will be greater than the value of the treasure. At that rate, you’d be better
off just getting a job as a contractor doing excavation work.
The most valuable single piece of traditional “treasure” in the world might be
a 12-gram gemstone known as the Pink Star diamond, which sold at auction in
2017 for $71 million. Seventy-one million dollars is enough money to hire a
contractor to dig for over a thousand years, or a thousand contractors to dig for
over a year. If you owned a 1-acre plot of land, and you knew the Pink Star
diamond was buried 1 meter deep somewhere on your property, it would almost
certainly be worth the expense to try to dig it up. But if your land were a square
kilometer in area and the diamond were buried several meters down, the cost of
hiring people to excavate would start to approach $71 million, and digging it up
wouldn’t be worth it.
At least, it wouldn’t be worth it if you were digging with shovels.
VACUUM EXCAVATION
If your planned excavation is large enough that it would take years to dig by
hand, then a shovel is almost certainly not the most efficient way to do it, and
you should consider slightly more modern techniques.
One more modern digging technique is vacuum excavation. Vacuum
excavation involves using what is effectively a giant vacuum cleaner to remove
the dirt. Suction alone isn’t powerful enough to pull apart tightly packed earth,
so vacuum excavation combines an industrial vacuum with a jet of high-pressure
air or water used to break up the ground.
Vacuum excavation is particularly useful when you want to dig up an area
without damaging underground objects such as tree roots, utility lines, or buried
treasure. The high-pressure air blows dirt out of the way but leaves larger buried
objects intact. Vacuum excavators can remove many cubic meters per hour,
potentially expanding the rate at which you can dig by a factor of 10 or more.
The largest holes are dug using mining excavators, which can remove
successive layers of land to create open-pit mines, holes shaped like an upsidedown layer cake. These holes can reach staggering sizes—the Bingham Canyon
copper mine in Utah features a central pit about 2 miles across and over half a
mile deep.
Oak Island, the site of the infamous money pit, is less than a mile across at its
widest point. If the Bingham Canyon excavation had occurred there—with the
installation of pumps and seawalls* to keep water out of the pit—excavators
could have removed the entire island and the underlying bedrock down to a
depth 10 times deeper than the deepest shaft dug by treasure hunters.
The material could be carefully sifted through to search for any treasure,
putting an end to the mystery once and for all.
THE BIGGEST HOLES
Using industrial excavation and drilling methods, humans are capable of digging
huge holes. We’ve removed entire mountains, created vast artificial canyons,
and drilled shafts a significant fraction of the way through the Earth’s crust. As
long as the rock is cool enough to work with, we can dig holes as deep as we
want.
But should we?
In 1590, more than 300 years before the Panama Canal was built, the Spanish
Jesuit priest José de Acosta discussed the idea of digging a channel through the
isthmus to connect the two oceans. In his book Historia Natural y Moral de las
Indias, he speculated about the potential benefits and pondered some of the
engineering challenges involved in “opening the earth and joining the seas.” He
ultimately decided it was probably a bad idea. Here’s his conclusion, from the
2002 translation by Frances López-Morillas:
I believe that no human power is capable of tearing down the strong and
impenetrable mountain that God placed between the two seas, with hills
and rocky crags able to withstand the fury of the seas on either side. And
even if it were possible for men to do it I believe it would be very
reasonable to expect punishment from Heaven for wishing to improve the
works that the Maker, with sublime prudence and forethought, ordered in
the fabric of this world.
Theological questions aside, there’s something to be said for his humility.
Humans are capable of unlimited excavation, from backyard shovel digs to canal
construction to industrial strip mining and mountain removal. And by digging
holes, we can certainly find things of value.
But perhaps—sometimes—it’s better to just leave the ground the way it is.
CHAPTER 4
How to Play the Piano
(the whole piano)*

Playing the piano isn’t very hard, in the sense that the keys are all easy to reach
and they don’t take very much force to push down. Playing a piece of music is
just a matter of finding out which keys you need to press, then pressing them at
the right time.
Most piano music is written using standard musical notation, which consists
of a series of horizontal lines with marks along them corresponding to notes. The
higher a note mark is, the higher-pitched the note. Most of the time, notes are
drawn in the middle of the lines, but particularly high or low notes sometimes go
off the bars to the top or the bottom. A piece of piano music looks something
like this:
The standard full-size piano has 88 keys, each of which corresponds to a
musical note, organized from lowest on the left to highest on the right. If you see
marks above the lines on your sheet music, you’ll probably need to press keys on
the right side of the piano, whereas marks below the lines will likely mean
pressing keys on the left.
A piano can play notes pretty far above and below the lines. In fact, it has one
of the widest ranges of any musical instrument, which means it can play all the
notes that most other instruments can.* If you memorize all the keys and all the
notes, then practice playing them in the right order with the right timing, you’re
all set—you can play any piece of piano music.
Well . . . almost any. The standard full-size piano may have a very wide range,
but there are still some notes it can’t play. To play those notes, you’ll need more
keys.
When you press a key on a piano, a hammer strikes one or more strings,
which vibrate and produce sound. The longer the string is, the lower-pitched the
sound will be. Technically, the sound made by each string as it vibrates isn’t just
a single frequency—it’s a rich mix of different frequencies—but each one has a
central “main” frequency. The main frequency of the sound made by the
leftmost key on a full-size piano is 27 hertz (Hz)—which means the string
oscillates 27 times per second—while the rightmost key’s main frequency is
4,186 Hz. The ones in between form a regular scale, spanning a range of about 7
octaves. Each key has a frequency roughly 1.059 times higher than the one to its
left—that’s 2
1/12
, which means that every 12 keys, the frequency doubles.
The upper limit of human hearing is quite a bit higher than 4,186 Hz. Young
children can hear sounds as high as 20,000 Hz. If we want to be able to play all
the notes humans can hear, we’ll need to add some keys to the piano. Covering
the range between 4,186 Hz and 20,000 Hz requires 27 extra keys.
As people get older, they typically lose the ability to hear some of the highest
frequencies, so you won’t need all the keys if you’re playing music for grownups. The rightmost handful will produce notes only audible to small children.
On the left end of the piano, covering the human hearing range is a little
easier. The lower limit of human hearing is somewhere around 20 Hz, 7 Hz
lower than the lowest key on the piano. To cover this range, we’ll need another 5
keys. This new, improved 120-key piano will allow you to play any piano music
humans are capable of hearing!
But we can extend the piano further.
Sounds above the range of human hearing are called ultrasound. Dogs can
hear sounds as high as 40 KHz, twice the highest frequency that humans can
hear. This is how “dog whistles” work—they produce sounds that dogs can hear
but humans can’t. Modifying your piano to play dog music will require adding
12 to 15 keys.
Cats, rats, and mice can hear even higher frequencies than dogs, and would
need several more keys. Bats—which catch insects by emitting pulses of
ultrasound and listening for the echoes—can hear up to around 150 KHz. To
cover the full range of hearing for humans, dogs, and bats would require a total
of 62 new keys on the right, for a total of 155 keys.
What about even higher frequencies? Unfortunately for us,* physics starts to
get in the way. High-frequency sounds are absorbed by air as they travel through
it, so they fade out quickly. That’s why nearby thunder makes a higher-pitched
“cracking” sound, while faraway thunder makes a low rumble. They both sound
the same at the source, but over a long distance, the high-frequency components
of the thunder are muffled and only the low-frequency ones reach your ear.
One hundred fifty kilohertz sound can only travel a few dozen meters in air—
which is probably why bats don’t use higher frequencies. Since attenuation is
related to the square of the frequency, higher ultrasonic pitches are substantially
more muffled. If you go too much higher than 150 KHz, the sound won’t be able
to travel very far beyond your piano. Ultrasonic sounds can travel farther in
water or solid material—which is how electric toothbrushes, medical
ultrasounds, and high-frequency whale and dolphin echolocation work—but
since pianos are typically used in air,* 150 KHz makes a pretty good cutoff.
The right side of our piano is complete. What about the left?
Sounds below the normal hearing limit of 20 Hz are called infrasound, and
they can be a little confusing to think about.
When individual sounds happen quickly enough, they blur into a single hum.
Imagine the sound of a bicycle wheel with something stuck in the spokes—at
low speeds, it makes a “click click click” sound, while at high speeds it makes a
buzzing hum. This suggests that low-frequency sounds shouldn’t really “fall
below the range of human hearing”—they should just separate into a series of
individual sounds. But that isn’t quite right.
When sounds are made up of complex individual “pulses”—like the raspy
sound of a playing card striking a bicycle spoke—they do separate out into
individual audible pulses, but only because those pulses are made up of higherfrequency components within normal hearing range. A pure tone, on the other
hand, is just a simple sine wave; the sound is made up of air moving smoothly
forward and backward. When it slows down to below 20 cycles per second, there
are no “clicks” to hear. It just becomes a pulsating pressure wave. We may feel
it, as a pressure change in the air or a sensation on our skin, but our ears don’t
interpret it as sound.
Elephants can hear infrasound. Their hearing reaches down to somewhere
around 15 Hz—and possibly lower—which means our piano will need at least
another 5 keys if we want to play elephant music.
Sounds below 15 Hz can be detected using specialized equipment. In fact, if
you’re interested in very low frequencies, you can technically make an
“infrasound microphone” with just a barometer and a clipboard. If you detect
low pressure, then high, then low again, that could be an infrasound wave!
A sequence of low and high pressures isn’t necessarily a “wave”—it could
also be a random pressure fluctuation in the air. That’s why, to detect these
sounds, researchers typically use an array of sensors spaced several meters apart.
When an infrasound wave passes by a detector, it will pass over all the sensors at
about the same time, which helps to separate out infrasound waves from random
noise. If the sensors are spaced widely enough, you can even figure out which
direction the sound came from by noticing which sensors registered it first.
Producing sounds like this would require a very large piano, because the
strings would need to wobble back and forth so slowly that you could watch
them move. (In a sense, a jump rope is just a stringed instrument with a
frequency about five octaves below the lowest standard piano note.)
Even though we can’t hear infrasound, it behaves like normal sound, carrying
signals through the air. In fact, while ultrasound travels less far than normal
sound, infrasound travels farther. An infrasonic signal with a frequency below 1
cycle per second—1 Hz—can travel all the way around the planet.
Sound recordings are sometimes plotted on a chart showing which sound
frequencies were detected at which times. You can produce a plot like this from
any sound recording, not just infrasound. In fact, the musician Aphex Twin has
hidden “images” in his music that can be seen on a spectrogram.
When a nuclear weapon goes off in the atmosphere, it creates a huge
infrasound pulse. Much of the work on infrasound detection happened during the
Cold War, as scientists built detectors to listen for those pulses. The last
atmospheric nuclear detonation, as of this writing,* was a weapons test in China
on October 16, 1980, so there haven’t been any explosions for the networks to
hear since then.
But an infrasound microphone picks up all kinds of interesting things beyond
nuclear explosions. Large pieces of machinery that move rhythmically, like
motors and wind turbines, create steady infrasound tones. Other infrasound notes
are played by wind rushing over mountains, meteors entering the atmosphere,
and even earthquakes and volcanic eruptions. A plot of atmospheric infrasound
will also show warbling tones of unclear origin. It’s just like regular sound
frequencies—if you go somewhere quiet and listen very carefully, you’ll hear all
kinds of interesting noises, only some of which you can identify.
One of the most common infrasound tones is produced by waves on the open
ocean. As the sea rises and falls, it presses rhythmically against the air, behaving
like the surface of a huge, slow music speaker—the loudest, deepest subwoofer
on the planet.
The sounds produced by the waves, called microbaroms, fall near 0.2 Hz.
Playing microbarom frequencies on our piano would require an additional 75
keys, bringing the total to 235.
That’s a lot of keys. But if you master them all, you can play everything from
Beethoven to bat hunting songs to the voice of the sea itself.
One last note: this piano will be difficult to construct. Piano strings won’t
work for producing ultrasound because the vibrations are too small and fade too
quickly—even within the normal range of pitches, pianos typically need multiple
strings for the highest notes in order to make them loud enough. Piano strings
are also not ideal for producing infrasound: the strings would be too long to fit in
a room and would have difficulty moving enough air around. For generating
high and low notes, you’ll want to use alternative techniques.
The most effective way to create ultrasound is through the piezoelectric effect,
in which a crystal vibrates when you run electric current through it. The
timekeeping element inside a digital watch or computer clock uses this effect: it
contains a tiny piece of quartz shaped like a tuning fork that vibrates at a precise
frequency in response to electric pulses. Similar quartz oscillators can be used to
produce ultrasound of any desired frequency.
For the infrasound speaker, you might want to make use of a mechanism
called a rotary woofer, a device that uses carefully controlled tilting fan blades to
gently push air back and forth. By changing the pitch of the fan blades, it moves
air forward, then backward, then forward again.
If you successfully manage to build the full 235-key piano, here’s a sample
piece for you to play. It will take some patience and it won’t sound like much to
your human ears.
But if any researchers out there are monitoring the atmosphere, listening for
meteor explosions or nuclear weapons tests . . .
. . . it will print out a stick figure on their spectrograph.
Infrasonata


CHAPTER 5
How to Make an Emergency Landing
A Q&A with test pilot and astronaut Chris Hadfield
How do you land a plane?
To answer this question, I decided to turn to an expert.
Colonel Chris Hadfield has flown fighter jets for the Royal Canadian Air
Force and worked as a test pilot for the US Navy. He has flown more than 100
different aircraft. He also flew two Space Shuttle missions, piloted a Soyuz,
became the first Canadian to walk in space, and served as commander of the
International Space Station.
I contacted Col. Hadfield and asked if he could offer some advice on
emergency landings, and he graciously agreed.
I made a list of unusual and improbable emergency landing scenarios, then
called him up and posed each one to him to see how he would respond. I half
expected him to hang up on me after the second or third question, but to my
surprise, he answered every one with virtually no hesitation. (In retrospect, my
plan to fluster an astronaut by throwing extreme situations at him might have
been flawed.)
The scenarios and Col. Hadfield’s answers—edited a bit for clarity and
brevity, including some additional answers by email—are presented below.
These aren’t necessarily the only possible ways to handle each task, but they
represent the first instinct of one of the world’s foremost test pilots and
astronauts, so they’re probably a pretty good place to start.
HOW TO LAND ON A FARM
Q: Suppose I need to make an emergency landing, and all I can see are
farm fields. Which crop should I aim for? Should I pick a taller one
that will provide more drag, like corn, or something low to the ground
to give me a smoother surface? Would a field of pumpkins provide
extra cushioning, like those barrels of water on a highway, or just make
me more likely to flip over and catch fire?
A: I fly little airplanes, and that’s something we think about all the time. When
you’re driving to your airfield, you look around, and think, how high are the
beans? Have they brought in their hay? Has it rained recently? You can’t
land on a muddy field.
You want something where the crop is not so tall or thick that it will make
your plane flip over. Obviously sunflowers would be a big mistake.
The best thing to land on is a freshly planted field. The worst place to land
is somewhere that’s just been plowed. Don’t land on ginseng. They have to
put up big sunshade structures and you’ll get tangled up in them. You’ve
gotta watch out for trees. Pastures are nice, but you have to be careful not to
hit the cows. Corn is ok to land in up until the middle of June.
HOW TO LAND ON A SKI JUMP
Q: What if I’m making an emergency landing in a small plane, but the
only open space I can find is an Olympic ski jump? What’s the best
way to approach it?
A: I was actually a ski instructor before I became a fighter pilot.
Olympic ski jumps are pretty dang high. There’s that little flat section at the
bottom, which would probably be your best bet. You could come in over
the stands, nice and slow, and get down close to the ground, then just as the
hill starts to rise in front of you, pull up. If you time it right, you could try
to stall the airplane at the exact moment that you hit the slope. But you’d
have to time it just right. If not, no do-overs.
HOW TO LAND ON AN AIRCRAFT CARRIER
Q: What should I do if I want to land on an aircraft carrier, but I’m in a
passenger plane not designed for carrier landings? Should I try to snag
my landing gear on the cable? How should I approach the carrier?
A: What you’re going to want to do is get the captain of the aircraft carrier to
turn her ship into the wind. Get the ship going as fast as she can make it go,
which might give you 50 or 60 mph winds. For a lot of little airplanes,
that’s enough speed that it will get you going pretty slowly relative to the
ship.
Get rid of those arresting cables; you don’t want to snag one by accident.
You need special gear to use an arresting cable. Unless you have a big
strong hook, then you’re going to want to do it completely
aerodynamically.
Then you need to get yourself lined up. You’re going to want to make use
of every inch of the flight deck. You should extend the flaps, changing your
wing from being flat to being sort of curved. If you watch birds land, they
do that with their wings. When you try to fly slow, you deploy your flaps.
You want to hit the aircraft carrier RIGHT at the very back of the deck.
Then you want to chop your power to zero, bring your engines back, and
raise your flaps immediately. Otherwise wind can blow you off. However
—keep your hand on the throttle. You want to be able to jam your throttle
up and go around again. In fact, when military pilots land on aircraft
carriers, they throttle up to full power right after they touch down, just in
case the hook skips over the cable or the cable breaks.
One project I did was for the US Marine Corps. They were thinking, “What
if we have an open space somewhere in the woods, but it’s too short to land
an airplane? Could we put a temporary arresting cable in the woods?” With
a cable strung between big stakes, you can stop and land anywhere. I tested
that system in Lakehurst, NJ.
HOW TO LAND ON A HOSTILE AIRCRAFT CARRIER
Q: What if the captain doesn’t want me to land? Would she turn to go
downwind, to make it harder?
A: There’s always stuff on the deck. If they don’t want you to land, they can
move stuff to block your way. There are lots of little carts that they use to
tow the airplanes around, and they could just drive the little carts out all
over the runway.
You’d have to sneak up on them and do it at the right time, and get lucky.
You might be able to do it. But I don’t think the captain would be happy.
And now what? You’ve just landed in the most heavily fortified jail in the
world, and declared yourself an inmate.
HOW TO LAND ON A TRAIN
Q: Could I land on a train by matching speed with it and gradually
bringing the plane down to rest on the roof of one of the cars?
A: Yes, you can do that. Flatbed truck, too. You see that at air shows
sometimes.
The hard part will be that, as you touch down, the train always moves up
and down a bit, which will bounce you. That’s the problem with landing on
a truck, too. But it’s absolutely doable.
HOW TO LAND ON A SUBMARINE
Q: Landing on an aircraft carrier sounds pretty easy. Could I land on a
submarine?
A: Yes, if it’s on the surface, driving fast into wind, and you have a slow, stable
airplane. Like landing on a skinny, short, wet runway. I think it’s been
done. Sometimes hard to find a submarine when you need one, though.
HOW TO LAND FROM THE COCKPIT DOORWAY
Q: What do I do if I somehow accidentally close my sleeve in the cockpit
door, and can’t reach the front of the cockpit? But I can reach some
objects—maybe trays of in-flight meals—that I can throw at the
controls. If I’m good at throwing, could I land by hitting the right
controls?
A: If it’s a single-engine plane, no way. But in a plane with multiple engines, it
might technically be possible. The way you’re going to control things is
power. If you have engines on each side, by moving the throttles up and
down you can climb, and you can turn that way, too. If you’re really careful
about throwing the utensils, you can fly an airplane just by moving the
throttles up and down.
There was a DC-10 that lost all hydraulics, over Sioux City, and the pilots
managed to get control and steer that airplane all the way around to the
runway using only the throttles.
HOW TO LAND A SPACE SHUTTLE IN DOWNTOWN
LA
Q: In a scene in the 2003 movie The Core, Hilary Swank plays an astronaut
in a Space Shuttle that has veered off course due to a navigation error.
She realizes they’re headed for downtown Los Angeles, and she plots a
course to land in the Los Angeles river—basically a long flat-bottomed
concrete canal. In the movie, they manage to land safely in the canal.
Could something like that really happen?
A: The Shuttle touches down around 200 knots—185 if you’re light, 205 if
you’re heavy. You need a long straight runway, thousands and thousands
and thousands of feet. We did the initial Shuttle landings on the huge salt
flats of Rogers Dry Lake at Edwards Air Force Base. Once we got better at
it, we started landing on a 15,000-foot runway.
What we really want to do is land where we take off, so we built a runway
at Kennedy which was 15,000 feet long. The runway at Edwards is way out
in the desert, so if you roll off the edge of the runway it’s not so bad. The
one at Kennedy has less room for error because it’s surrounded by water
and there are alligators.
When you’re coming in to land at Edwards, you have to do the deorbit burn
all the way back over Australia. The computer calculates the timing to bring
you down over your landing site. But with enough planning, you could land
on any long, straight, flat surface. Landing in Los Angeles drainage
ditches? I’m not sure there are any that are long enough.
You might have to deorbit anywhere in the world. We identify every
runway in the world. We carried a book in the Shuttle with diagrams of all
of them. It’s like a big picture book. It shows the orientation of the runway
and everything.
HOW TO FIND A PLACE TO LAND THE SHUTTLE
Q: If I’m not sure how to use the computer, could I just guess? Could I fire
the engines somewhere over Australia, figuring that will bring me down
in the right part of the world, and then look for a good landing site out
the window as I get close? How much room in a landing do I have to
improvise?
A: There’s a fair bit of room! We fly big S-turns to bleed off energy. If we fly
fewer turns we could fly farther. The closer you get, the less ability you
have to change your mind. But it’s not completely far-fetched. You have a
chance, if you aim for a general area and eyeball things.
When they were flying the X-15, a Shuttle predecessor, pilots would try and
make the test flights last as long as possible. Neil Armstrong ended up too
low over Pasadena and had to land on the wrong lake bed. I’m glad he
made it.
HOW TO LAND A PLANE FROM THE OUTSIDE
Q: Say I’m locked out, on the exterior of the plane, but I can crawl around
and manipulate the flight control surfaces by hand.
A: People do wing walk, and occasionally people have done that to fix stuff. In
an old, slow airplane, wind speed is low enough to stand on the wings.
What you could do is use your own weight. You could control where the
airplane is going by moving your weight around. Just move your weight to
the right side, and the plane might begin a right turn.
If you can talk to the passengers inside, you could try to get them to run to
the front or the back, and you might be able to control it a little bit that way.
But if you want to mechanically control the airplane, you have to get back
to the tail. If you’re on the wing you can only control roll—you can’t
control pitch or yaw. Roll is nice, but pitch and yaw are more important. To
control pitch and yaw, you go back to the tail.
The problem is, you can’t move those control surfaces by hand. No one is
strong enough. If you were the Hulk, you might be able to find a handhold
on the front of the tail with one hand and use the other to move the fin, and
you could turn the plane left and right. Then you reach down and grab the
elevator and do the same thing to control pitch. Conceivably, if you were
good enough, you could use those to fly the airplane down.
Since you’re not the Hulk, what you might do, if you were a little clever, is
to find the trim tab. The trim tab is a little flat section on the edge of the
surface that you use to make fine adjustments. You could move the trim
tab, and it moves the whole elevator or the whole rudder.
HOW TO FLY THROUGH THE CHUNNEL
Q: Suppose I’m flying a very small aircraft like a Colomban Cri-Cri
(wingspan: 16') over southern England right when Brexit happens. For
complicated legal reasons, this means I need to land in France.
Unfortunately, I’m a vampire who can’t cross the water of the English
Channel. Could I fly through the 25'-diameter Chunnel?
A: Yes—but 25' diameter and 16' wingspan means max clearance of 4.5' each
side if you’re right dead center. You could only climb or descend a few feet
before your wingtips would hit concrete (you can do the math). The hardest
part might be avoiding all the overhead wires at the Chunnel entrance and
exit. And it would be dark, so you’d need to put lights on your Cri-Cri, or
ask the nice Chunnel people to put all the lights on. But . . . for the tasty
croissant and coffee at the landing aérodrome, it might be worth it.
HOW TO LAND DANGLING FROM A CONSTRUCTION
CRANE
Q: If I’m flying an aircraft with a tailhook near a large construction crane,
could I land by rolling onto my side and snagging the hook on the
crane’s dangling cable, then—once I’ve stopped swinging—have the
crane operator gently lower me to the ground?
A: Maybe, if you’re very lucky. Planes get snagged in power lines all the time
and survive, where the crew have to be lowered by crane. But the inertia of
your tailhook plane would likely be too much for the cable, and you’d snap
it, plus even if you get snagged sideways, what keeps you from slithering
down and hitting the ground? I’d go for power lines instead, and hope you
don’t cross the wrong wires and get electrocuted.
HOW TO GET OUT OF YOUR PLANE AND INTO ONE
THAT HAS MORE FUEL
Q: Say my friend and I are flying a pair of small aircraft over a sharkfilled ocean. I’m about to run out of fuel, but I have a parachute. My
friend is flying alongside me. Could I get out of my plane and into
theirs, then land that plane?
A: If they are open-cockpit biplanes, then maybe yes. You could trim your
plane’s controls to fly hands-off, get your friend very close, climb out on
your wing, reach out and grab the wing of the other plane, and clamber into
the cockpit. Needs to be an open cockpit so you don’t have to deal with a
canopy/doors, and a biplane so there are struts as handholds. If you jumped
out of yours and hoped your buddy would somehow snag you as you
floated under your parachute, my guess is you’re shark lunch.
HOW TO LAND A SHUTTLE IF IT’S ATTACHED TO
THE CARRIER AIRCRAFT
Q: Suppose I’m riding in the Space Shuttle while it’s being carried by the
Shuttle Carrier Aircraft. The carrier aircraft is on autopilot, but the
pilot has decided to abruptly retire and has bailed out. What do I do? I
assume if I have a parachute, I’d bail out from the Shuttle’s exit hatch,
but what if I don’t? Should I try to detach the Shuttle, or get from the
Shuttle into the carrier aircraft?
A: The initial flights of the Space Shuttle were drop tests from the Shuttle
Carrier Aircraft. So I’d wait until you’re within gliding range of a suitable
runway, fire the separating mechanism from the SCA, pull back firmly to
miss the SCA’s tail, and then glide to a landing. Easy peasy.
HOW TO LAND IN THE INTERNATIONAL SPACE
STATION
Q: What should I do if I accidentally get left behind on the ISS when it’s
being deorbited? I know large objects occasionally survive uncontrolled
reentry intact. If I find a parachute, where in the ISS should I hide to
have the best chance of surviving to the point where I could parachute
down?
A: You want a blunt, heavy piece of metal, and you need to have your own
oxygen supply. So best bet is to get into a Russian Orlan spacesuit (you can
easily self-don), get it running so you have pressure, cooling, and oxygen,
jury-rig a parachute to it, and go into the FGB (Functional Cargo Block).
Strap yourself to the thickest metal part near the middle, where there are the
most massive things under the floor, batteries and structure, aligned with the
solar array attachment points—and wait to see what happens. But . . . odds
are slim to none.
Maybe bring your rosary beads so you have something optimistic to do
while you wait.
HOW TO SELL PARTS FROM A PLANE MID-FLIGHT
Q: Say I decide I want to land a plane, but first I want to sell as many
parts as I can on Craigslist. I decide that shipping is too expensive, so I
want to deliver them before I land by removing them from the plane
and throwing them overboard as I pass over the buyer’s house. How
much of the plane can I sell and still land safely?
A: All the food. All the seats. But you have to be careful to keep your center of
gravity in limits. If the center of balance is too far forward, then it becomes
like a dart—no matter how hard you pull back on the stick, it’s going to
want to nose down. If the center of gravity gets too far aft, your aircraft
becomes super unstable. Definitely get rid of all your cargo. Everything in
the baggage compartment is something that someone paid to transport, so
it’s probably worth something.
HOW TO LAND A FALLING HOUSE
Q: When spacecraft like the Soyuz are returning to Earth, once they open
up their parachutes they have no more control—you’ve described this
phase as “falling like Dorothy’s house.” In The Wizard of Oz, when
Dorothy woke up to find her house plunging toward Oz, can you think
of anything she could have done to control her descent? Like if she
looked out the window and saw the witch below, and wanted to miss
her, or hit her, or aim for someone else?
A: I suppose she could have tried to run around and open windows and doors
on different sides of the house, to see if she could have some aerodynamic
control by changing the airflow. But I don’t imagine it would be easy.

HOW TO LAND A DELIVERY DRONE
Q: Suppose I’m picked up by a malfunctioning quadcopter-style delivery
drone, which hooked my jacket with its carrying arm and is heading up
and out toward the ocean. I can extricate myself and climb up to reach
the drone body, but how should I try to force it down gently without
crashing?
A: Drones are battery-powered, so if I were you I’d pop the battery loose, let
the drone fall a bit, stick the battery firmly back in, and play that until I can
judge the descent, then choose a good moment to jump off. Best would be
just after it got over water, in the shallows.
HOW TO LAND A ROC
Q: One last question. I know this might be outside your area of expertise,
but suppose I’m picked up by a roc—the giant mythical bird. How
should I try to force it to put me down without dropping me?
A: Your best bet is treat it like a big angry hang glider. If you pull yourself way
off to one side, the roc will have to turn in that direction. If you somehow
fling your weight forward, it will have to dive. If you were strong enough,
you could sort of steer it, like a big, noncooperative glider.
The other thing you could do, if you have anything with you, like a tent or a
lot of clothing, is you could deploy a parachute of sorts. Just the added drag
of a parachute, or any big object hanging down, will irritate the heck out of
any creature trying to fly. If you’re a skydiver, deploy your parachute.
You’ve always got your reserve chute.
You can start clipping its wings if you’re armed. It depends whether you’re
willing to go on the offensive.
What you might want to do is be psychological. What does it want? Do you
have food? What you don’t want is for it to become irritated and let go of
you. What it needs to do is be motivated to keep carrying you. I think I
would try to get to a part of its body where it couldn’t get me off. If I could
get up behind its back and hold on, as long as you’re holding on tight
enough, it can’t reach there. Like a bug it can’t scratch. But if you’re trying
to modify its flight plan, either you’ve gotta use your own weight or use
your own psychology or intellect. I don’t know what motivates a roc.
Randall: Thank you so much for agreeing to answer these questions.
Col. Hadfield: Thank you for the . . . interesting . . . questions. I hope no one
ever has to use my answers! But if you do—tell Randall so he can update this
book.
CHAPTER 6
How to Cross a River
Humans like to live near rivers, which means we often find ourselves needing to
cross them.
The simplest way across a river is to ford it—which effectively just means
pretending it’s not there, continuing to walk, and hoping for the best.
People usually try to ford rivers at areas where the river is pretty shallow, but
even shallow water can be surprisingly dangerous. It’s not always easy to tell
how fast water is moving, and it only takes ankle-deep water to sweep a person
off their feet.
If the river is too deep to ford, you can try swimming across. But whether
swimming works or not depends a lot on the river conditions. If the river is
moving too fast, you could be pushed around by the current, swept downstream,
or sucked under obstacles or into rapids.
A normal person who knows how to swim—but isn’t an athlete or anything—
can probably move along at a few feet per second. This is much faster than some
rivers and much slower than others—river speeds range from less than a foot per
second to more than 30 feet per second.
If the river were an idealized region of water moving in a straight line at a
constant speed, the time it took to swim across would be easy to figure out, since
you could just swim directly toward the opposite bank and ignore the current. A
faster-moving river would carry you farther downstream in the process, but
you’d still reach the opposite bank in the same amount of time.
Unfortunately, real rivers don’t flow at a uniform speed. Water tends to go
faster in the middle than at the edges, and faster near the surface than at the
bottom. The fastest-moving parts are usually over the deepest parts of the river, a
little under the surface. For a smooth, uniform river flowing in a straight line, the
speed might look like this:
A riverbed with wide flat areas and deep channels might look more like this:
If you tried to swim across one of these rivers, your path would look more
complicated. Moreover, real rivers don’t flow in a straight line. They have
eddies and whirlpools and currents that meander back and forth. In a real river,
you might find the current keeps pushing you away from the bank, or sucks you
under, or carries you downstream and over a waterfall.
That sounds dangerous. Let’s take a look at some other options.
JUMP OVER IT
If swimming through the river doesn’t appeal to you, you can try going over it.
The simplest way, if the river is small enough, is to jump.
There’s a simple formula for determining how far a projectile can fly when
launched diagonally under ideal conditions.
The exact distance you can jump depends on the details of your approach,
launch, and landing, but this formula gives a pretty realistic estimate of what’s
possible. Based on the formula, if you run at 10 mph, you can expect to jump a
gap of up to about 7 feet. This confirms that, for very small streams, jumping
across is certainly an option.
You can increase your distance by increasing your speed, which is why
champion long jumpers are sometimes also champion sprinters—in a sense, a
long jumper is just a sprinter who’s good at briefly going up instead of forward.
Elite long jumpers can jump nearly 30 feet, which involves accelerating up to a
sprinting speed of well over 20 mph shortly before takeoff.
Bicycles are faster than sprinters. If you get on a nice bicycle and pedal hard,
you might be able to accelerate to about 30 mph. At this speed, you could—in
theory—jump across a 60-foot river.
Unfortunately, thanks to conservation of energy, if you’re going 30 mph when
you take off, you’ll be going 30 mph when you come down on the opposite
bank. That’s easily fast enough to cause serious or fatal injuries. It might
actually be safer to try this stunt on a river that’s wider than 60 feet. If you try to
jump an 80-foot river instead of a 60-foot one, you’ll land in the water near the
far side, which would probably be less damaging to your body than landing on
solid ground.
At least, assuming the water is deep enough.
Faster vehicles can of course jump farther. A car going 60 mph could in
theory jump a gap nearly 240 feet wide. However, landing a car at 60 mph is
unlikely.
Motorcyclist daredevil Evel Knievel made a name for himself jumping over
things with motorcycles, and famously attempted to jump the Snake River
Canyon on a rocket bike which, for legal reasons, was technically classified as
an airplane. Accounts differ on exactly how many bones Knievel broke during
his career, but his ratio of SUCCESSFUL MOTORCYCLE JUMPS : BROKEN BONES was
not large, and might have been less than one.
On second thought, maybe you should leave the jumping to the professionals,
and then maybe the professionals should decide not to do it either.
GO ACROSS THE SURFACE
People can’t walk on the surface of liquid water, at least not without the help of
technology or supernatural forces.
There are viral internet videos of people running across water, riding bikes
across water, and riding motorcycles across water. The basic principle behind all
these stunts is simple: if you go fast enough, when you hit the water you’ll ski
across. These videos usually go viral because they seem at least sort of plausible,
and the matter stays unsettled until the perpetrators of the hoax confess or the
MythBusters try it out.
Here’s a quick rundown of which types of stunts are real and which are fake:
As people who do barefoot water skiing know, staying above the surface
requires your feet to move at about 30 or 40 mph relative to the water. Even
Usain Bolt’s feet don’t move that fast when he’s sprinting.*
A bicycle won’t work either. You can figure that out, without trying it, simply
by asking an experienced cyclist. A cyclist can tell you that bicycles, unlike cars,
generally don’t hydroplane. They might slip on wet pavement, but because of the
curved shape of the tires, which push water away to either side, a bicycle tire
doesn’t lose contact with the ground and “surf” on a layer of water.
Motorcycles, which have flatter, treaded tires like cars’, can hydroplane, and
MythBusters has dramatically confirmed that they can also be used to cross short
stretches of water. But that’s taking us back into Evel Knievel territory.
Of course, there are specialized vehicles designed to travel over the surface of
water.
If you have a boat, it’s a perfectly good option. In fact, some rivers have boats
permanently stationed to ferry people back and forth between opposite sides.
OTHER PHASES OF MATTER
When we said people can’t run across water, that wasn’t quite true. They can’t
run across liquid water. But water has other forms. Let’s take a look at the other
phases of matter, and see whether we could convert the river into them in order
to make it easier to cross.
Freezing
To freeze a river, you’ll need some refrigeration machinery and a source of
power.
Thinking about the energy involved in freezing can be tricky. In a strict sense,
turning water into ice doesn’t take energy. When water freezes, it emits energy.
So if it takes energy to boil water, but freezing water gives off energy, why
does our freezer use electricity instead of generating it?
The answer is that the heat in water doesn’t want to leave. Heat energy
naturally flows from warmer areas to cooler ones. When you put ice cubes in a
warm drink, the heat leaves the drink and flows into the ice cubes, warming the
ice while cooling the drink, bringing them both toward equilibrium. The second
law of thermodynamics says that heat energy always wants to flow in this
direction: the ice never spontaneously heats up the drink while getting colder.
Moving heat from a colder area to a warmer one, against this natural flow,
requires a heat pump, which takes energy to operate. When you try to remove
heat from a river to lower its temperature and freeze it, you have to do work.
We can use estimates from commercial ice makers to figure out how much
energy it would take to turn a river to ice through refrigeration. The US Office of
Energy Efficiency and Renewable Energy, in its guide to estimating commercial
ice machine power consumption, suggests a default estimate of 5.5 kilowatt
hours (kWh) for every 100 pounds of ice produced. A normal spring flow rate
for the Kansas River at Topeka might be 7,000 cubic feet per second, which
gives us an estimated power of 87 gigawatts.
Eighty-seven gigawatts is a lot of power;* it’s equivalent to the power output
of a heavy-lift rocket as it takes off. Powering your refrigeration devices would
take a similarly large generator, and that generator would take a lot of fuel. In
fact, the flow rate of fuel into that generator would be about 300 cubic feet per
second, which is nearly 5 percent of the flow rate of the river itself.
In other words, your freezing apparatus would need to be fed by a river of
gasoline that is comparable in size to the river you want to freeze.
But maybe there’s a way around this. Maybe you don’t need to freeze the
entire river. You could just freeze the surface.
As a general rule, ice needs to be at least 4 inches thick before it’s safe to walk
on. The Kansas river is about 1,000 feet wide, which will be the length of the
bridge, so if we want to make the ice bridge 200 feet wide (to keep it from
bending and breaking), then our ice bridge will be roughly 2,000 tons. Freezing
that much ice would require about 330 megawatt hours of electricity, at a cost of
about $50,000 (not counting the cost of all the ice machines.)
Boiling
We’ve covered the solid and liquid options. What about gas? Could you install
some machinery upstream to convert the river from liquid to gas, then walk
across the dry riverbed?
No, you couldn’t. But let’s find out why.
First, you’d need a way to heat the water. Obviously, you can’t just use
ordinary teakettles. Instead, you’d need to—
Ok. If you want to boil the Kansas river using ordinary teakettles, here’s how
to do it.
A typical teakettle holds 1.2 liters of water. Water has a high heat storage
capacity—it takes a lot of energy to raise its temperature. But it takes a huge
amount of energy to transform it from hot water to steam. Heating a liter of
water from room temperature to 100°C takes about 335 kilojoules of energy.
Pushing that 100°C liquid over the edge into becoming 100°C vapor takes a
much larger 2,264 kilojoules.
You can see this effect when you boil water. It only takes about 4 minutes for
most electric kettles* to heat water to a boil. But when you turn off the heat,
most of the water is still there—it’s at boiling temperature, but it’s still in liquid
form. If you want to fully boil the water—turn it completely to vapor—then you
have to keep heating it for a total of about 30 minutes. This is much longer than
the 4 minutes it takes to start it boiling.
The Kansas River’s flow rate is 7,000 cubic feet per second, which works out
to roughly 10 million teakettles per minute.* Since each kettle would need to
boil its 1.2 liters of water for 30 minutes, you’d need a total of 300 million
teakettles running in parallel to boil it.
If an electric kettle has a 7-inch circular base, you can pack them at a density
of 3 per square foot.
Three hundred million kettles will take up a circular area 2 miles in diameter.
To boil the river, you’ll have to split it up and divert its flow across your kettle
field. Each kettle will boil the water as it flows in, and once a kettle is empty,
fresh water from the river will replace it.
Here’s how this method would work in theory:
Now, here’s how it would actually go:
Your electric kettles would draw roughly as much electricity as the entire rest
of the country combined. There’s no way you could get that much power
focused on one location like this using our electric grid.
Which is probably for the best. Because if you could, things would not go
well.
Boiling water creates hot steam. Steam rises. With a single kettle in a kitchen,
that’s fine—the steam rises, hits the ceiling, spreads out, and eventually
disperses.
In a sense, this is also what would happen to your kettle field. But the
experience would be a little more . . . dramatic. The column of steam would
build into the stratosphere, spreading out and forming a mushroom cloud, like a
volcanic eruption or nuclear explosion. When air rises, more air flows in from
the side to take its place. You might not notice this when it happens over your
stove with a single kettle, but the people living in Kansas around your kettle
field would definitely notice. From all directions, winds would blow across the
surface toward the kettles, converging on the base of the rising steam column.
Down at the base, things would not be going well. The kettles would be
absorbing a huge amount of electrical energy and dumping it back out in the
form of steam and heat radiation. The energy output of your kettle field would
be greater than the heat output of a miles-wide lake of lava.
Heat is something of an equalizer. As a rule of thumb, anything that puts out
as much energy as a lake of lava becomes a lake of lava. Your kettles would
overheat, break down, and melt.
Say you manage to find fireproof, heat-proof kettles and wires. Then the
kettles may start heating the lower layers of steam too fast. The heat would flow
in faster than convection could carry it out, and the temperature of the steam
would rise. Potentially, if you ran the kettle field long enough, the steam could
begin turning from gas to plasma.
Here’s what it will look like when you try to cross the river:
As you walk through the mud of the riverbed, you see a giant column of steam
to your left, radiating intense heat, with a growing lake of lava at its base. From
your right, a powerful wind blows along the riverbed. The wind cools you, for
now, but if it gets too strong it might blow you toward the lava lake. From
above, a gentle rain falls, turning the ground into warm mud. Overhead,
electrical wires crackle and spark, as the entire US electricity grid shunts power
into your lava lake.*
At this point, you realize: you never even needed to turn the kettles on. It took
30 minutes to fill them with water; you could have used that time to let a section
of the river drain and walk across.
But that wouldn’t have been nearly as much fun.
KITES
If you don’t have 300 million teakettles,* you may want to try crossing the
river by kite.
Kites actually have a bit of a history when it comes to river-crossing. When
engineers wanted to build a suspension bridge across the gorge below Niagara
Falls, they needed to start by getting a single cable to run from one cliff to the
other.
They brainstormed ideas for how to get a cable across. They thought about
having a ferry go across towing a cable, but the river was too turbulent and fastmoving for the boat to make it without being swept far downstream. The gap
was too wide to shoot an arrow across, and they considered and rejected cannons
and rockets. Ultimately, they decided to hold a kite-flying contest, and offered a
$10 prize to whoever could fly a kite from one side of the gorge to the other.
After several days of effort, 15-year-old Homan Walsh succeeded in bridging
the gorge. He launched his kite from the Canadian side and managed to get it
snagged on a tree on the American side, winning the cash prize. The bridge
engineers used the string to pull a stronger string across the gap, and after
several more iterations, they had the two countries bound together by a half-inch
cable.* Then, they started running more cables across the gap, built a pair of
towers, and eventually constructed a suspension bridge.
Of course, if you’re going to go the Homan Walsh route, you can simply cut
out the middleman and fly yourself across on the kite. Human-lifting kites were
briefly pioneered in the late 1800s and early 1900s, before the invention of the
airplane made them seem slightly less exciting.
Of course, not every flight on a human-lifting kite ends in a terrible crash due
to changing winds. Sometimes, they crash for totally different reasons!
In 1912, Boston kite maker Samuel Perkins was testing a human-lifting kite in
Los Angeles. He was soaring at a record altitude of 200 feet when a passing
biplane sliced through the kite line. Miraculously, the fluttering kites acted as a
parachute, and Perkins survived his plunge with minimal injuries.*
You could also use a balloon in place of a kite. Balloons and kites are
strangely similar—a balloon on a string is, in a sense, a kite mirrored around a
diagonal line. A kite on a string “wants” to lie flat against the ground due to
gravity, and wind flowing past creates an upward force on the kite. Its final
diagonal angle is a compromise between the two forces.
A balloon, on the other hand, “wants” to go straight up, and wind pulls it
sideways. Again, the final angle is a compromise between the two forces. But as
wind grows stronger, kites fly more vertically, while balloons fly more
horizontally.
Once you’re across the river, your challenge is getting down. But this is easy:
for once, gravity is firmly on your side. You just have to make whatever’s
holding you up—kite, balloon, or other contraption—slightly less good at flying,
and gravity will do the rest.

CHAPTER 7
How to Move
You’ve picked a place to move to, and now you need to get all your stuff there.
If you don’t have very much stuff, and you’re not moving very far, this will be
easy. You can just put your stuff in a bag and carry it from your old house to
your new house.
Unfortunately, if you have a lot of stuff, moving can be a lot of work. At some
point in the move, many people take a look at all their possessions, realize how
much work will be involved in moving, and realize that it would be easier to
push everything into a hole and walk away, leaving it all behind. This is
absolutely an option! Should you decide to take this route, turn to chapter 3:
How to Dig a Hole.
If not, you’ll need to pack up your stuff. The standard packing method, chosen
by most people, is to put all your stuff in boxes and then carry the boxes out of
the house.
Unless you’re moving to your front yard, you’re not done yet. You’ve only
moved your stuff about 50 feet; depending on where you’re moving, you could
have hundreds of miles left to go. How do you get it there?
Carrying your stuff by hand is also a bad idea. Let’s say you can walk while
carrying about 40 pounds. As a general rule of thumb, all the furnishings and
possessions in a typical 4-bedroom house will weigh around 10,000 pounds,
which means you’ll need to take a total of 250 trips.* If you have 3 people
helping you, and you can walk 10 miles a day,* it will take you 7 years to move.
Things would be much easier if you could just make a single big trip with all
the stuff at once. The good news is that, in a frictionless vacuum, pushing stuff
sideways doesn’t take any work at all. And if you’re moving downhill, the move
will actually require negative work—you’ll get energy back! The bad news is
that you probably don’t live in a frictionless vacuum. Most people don’t, despite
the clear advantages one would offer when moving.
In our frictional air world, moving does take work. Your 10,000 pounds of
stuff is heavy, and pushing it sideways takes force. The drag force exerted by the
ground is simply the coefficient of friction between your boxes and the ground
times the weight of the boxes. To estimate the coefficient of friction, we can see
to what angle we have to tip it in order to make it slide, then calculate the inverse
tangent of that angle.
For a box sliding on a cement slab, the coefficient of friction might be 0.35,
which means we’ll need 3,500 lb of sideways force to move the boxes across the
ground. This is too much for one person—it’s about the force exerted by a 15-
person elite tug-of-war team*—but it’s within the capability of a large pickup
truck.
Pushing a 10,000-pound load 200 miles takes about 5 gigajoules of energy,
which is roughly equivalent to the electricity used by a typical house in 60 days.
If you’re using an elite tug-of-war team, that’s 600 daily 2,000-calorie rations.
Five gigajoules sounds like a lot, but it’s not—it’s only 40 gallons of gas.
Even if you have a truck powerful enough to push all your possessions across
the country, this is probably a bad way to move. As the cardboard slides on the
road, it will wear away, and your possessions will slowly be ground down.
You can improve the situation by putting all the possessions on a sled made of
some kind of hard, friction-resistant material. But you can improve the method
even more by placing rollers under the sled that move with it. Now, add an axle,
so you don’t have to keep replacing the rollers. Congratulations, you’ve
developed the wheel!
At this point, you’ve effectively reinvented the moving truck, which is the
standard method for moving. But all that packing is still a lot of work. If you
absolutely refuse to pack your stuff,* you have another option: move the entire
house.
MOVE WITHOUT PACKING
Houses are relocated all the time. Sometimes, a house is moved to preserve it for
historical reasons. Sometimes, it’s cheaper to bring a vacant house from
elsewhere than to build a new one from scratch. And sometimes, someone
decides they want to move a house, and if they have enough money to do it, then
they can just do it and they don’t have to explain why.
Houses are heavy—a house weighs a lot more than all the stuff in it. A
house’s weight varies a lot, but could be around 200 lb/ft
2
including the
foundation. Without the foundation, it might be significantly less. An averagesize single-story home might weigh 150,000 lb, or 350,000 lb with the concrete
foundation and/or concrete slab.
Lifting a house is difficult for reasons beyond the weight. A house might feel
solid, but it can be less rigid than you expect. Some contractors compare it to
lifting a king-size mattress—if you try to lift it from just one spot, only that spot
will come up.
To lift up a house, you generally need to cut holes in the foundation and place
I-beams under it, aligned with the load-bearing parts of the house. Then you can
lift those beams, lifting the house with them.
You’ll need to detach the house from its foundation first, which means
removing any “hurricane ties” between the foundation and the frame of the
house. Those ties are there to stop a hurricane from doing exactly what you’re
trying to do right now.*
Once you’ve lifted the house off its foundation, you’ll need to find a vehicle
to put it on—flatbed trucks are the most popular option. Then, you can use this
truck to drive the house to its new location, assuming the roads are wide enough.
Try not to take any turns too sharply.
Driving a house is harder than driving a car.* Unless your house is unusually
lightweight and aerodynamic, your gas mileage will probably suffer. How many
miles per gallon can you expect? Well, we can estimate that using some basic
physics. Modern internal combustion engines can convert about 30 percent of
the input fuel energy into useful work. At highway speeds, most of the engine’s
work goes into fighting air resistance, so to figure out how much fuel your
vehicle will consume, we just need to plug your house’s parameters into the drag
equation. (Since there are other sources of drag in addition to airflow, this is
probably a best-case scenario.)
I really love that we can ask physics ridiculous questions like, “What kind of
gas mileage would my house get on the highway?” and physics has to answer us.
Drag increases quickly at higher speeds. If you’re traveling at 45 mph, you’ll
get 0.8 miles per gallon. At 55, just a little faster, your efficiency will drop to 0.5
mpg. If you take your house out on the Autobahn and drive at 80 mph, you’ll 0.2
mpg, burning a gallon of gas every 1,200 feet that you travel.
You probably shouldn’t drive your house that fast, since 80 mph winds can
remove important pieces of your roof. Even if you’re under the speed limit, the
police might not be happy about someone recklessly driving a house.*
If you are pulled over, you might try arguing that you’re inside the house, and
police can’t come in without a warrant! In the United States, police officers are
allowed to search vehicles based on probable cause, but not homes. It’s the
perfect crime!
The legal system may disagree. In the 1985 case California v. Carney, the
Supreme Court ruled that motor homes and RVs, even when parked, qualified as
vehicles and could be searched without a warrant. In their opinion, they cited
mobility and roadworthiness as the key factors in determining whether
something was a vehicle and could be searched.
The capacity to be “quickly moved” was clearly the basis of the holding in
Carroll, and our cases have consistently recognized ready mobility as one
of the principal bases of the automobile exception.
—California v. Carney, 471 U.S. 386 (1985)
As far as I know, no court has ruled on the specific question of whether the
vehicle exception applies to a house being transported on a flatbed truck, but be
aware that you might be on shaky legal ground.
FLYING HOME
Maybe you’ve discovered some obstacles while planning your drive—like low
overpasses or narrow roads. Maybe you don’t want to apply for the “wide load”
permits. Or perhaps you’re in too much of a hurry to drive. If so, you could try
flying.
Moving your entire house by air presents some challenges. The most powerful
helicopters in the world can lift between 20,000 and 50,000 lb. That’s enough to
carry the 10,000 lb of possessions in a medium-size house, but not the house
itself.
If one helicopter can’t lift your house . . . could several? If you hitched
multiple helicopters to your house and had them all lift at once, would they be
able to lift a heavier load?
A multi-helicopter lift would present a few challenges. The helicopters would
have to pull in different directions to avoid colliding, which would reduce their
overall capacity. They would also need to coordinate carefully to avoid
collisions. But you could solve both these problems by attaching the helicopters
together rigidly, so they lifted as a single aircraft.
This idea sounds ridiculous, so, unsurprisingly, the US military studied it
during the Cold War. In a 178-page report, they analyzed the idea of producing a
super heavy-lift helicopter by the sophisticated engineering technique of taking
two helicopters and gluing them together. The project* never went past the
planning stages, possibly because the engineering diagrams looked a lot like
mating dragonflies.
Cargo airplanes can lift more than helicopters. A large aircraft like the C-5
Galaxy can lift nearly 300,000 lb, enough to carry a medium-size house—and
possibly even the foundation, if the house is on the small side. Size might be
more of a problem than weight—most houses are too large to fit inside a C-5
Galaxy’s cargo hold.
There are a few whale-shaped specialty aircraft designed to carry unusually
large pieces of cargo. The largest, such as the Boeing Dreamlifter and the Airbus
Beluga XL, are built to transport pieces of other airplanes between factories
while they’re being constructed. If you ask nicely, maybe Airbus or Boeing will
let you borrow one.
If you can’t fit your house in an airplane, you could try putting it on one.
That’s how NASA transported the Space Shuttles across the country using a
specialized Boeing 747 which carried the Shuttle on its back. To carry the Space
Shuttle orbiter, the carrier aircraft has a special mount that protrudes from the
top of the fuselage. This mount fits into a socket in the belly of the Shuttle
orbiter. Next to the mount is an instructional plaque, which features the single
best joke in the history of the aerospace industry:
ATTACH ORBITER HERE NOTE: BLACK SIDE DOWN
Keep in mind that attaching your house to the outside of a carrier aircraft
would subject it to 500 mph winds, which is far beyond what most structures are
built to withstand. It would also probably affect the plane’s handling.
There’s another problem with moving your house by airplane: unlike a cargo
helicopter, which can take off and land vertically, an airplane can’t move your
house without knocking down a lot of telephone poles, trees, and neighboring
houses. If you don’t live at the end of a runway, taking off will be a problem.*
But if all you want to do is push your house into the air and then push it
sideways, why do you need the entire airplane? Why not just the pushing part?
The engines on a 787 Dreamliner can produce 70,000 lb of thrust and only
weigh 13,000 lb, which means two of them could lift a small house into the air.
The application of this is obvious.
You might think that airliner engines wouldn’t be very good at hovering in
place. After all, engines need oxygen to burn, which they pull in through those
big intakes in the front. It seems like they should be less efficient at scooping up
air when they can’t use their forward motion to help. But most turbofan engines
produce their maximum thrust when they’re sitting still. At higher speeds, the
engine does take in air more efficiently, but the extra drag from all that incoming
air counteracts the extra thrust the engine produces. Only at very high speeds,
near Mach 1, does the ram effect cause the engine thrust to increase again.
Two engines might, in theory, be enough to get your house into the air, but
you probably want to add a third and fourth for safety and stability.
Ok, you’ve got your house in the air. How long can you hover and fly around
like this?
When hovering, jet engines need a lot of gas. At full power near sea level,
each one consumes almost a gallon of jet fuel per second. Carrying more fuel
lets you hover longer, but it also means you’re heavier. If you add too much fuel,
you’ll be too heavy to lift off.
To figure out how long this kind of vehicle can hover if loaded with the
maximum amount of fuel, you multiply the engine’s specific impulse by the
natural log of its thrust-to-weight ratio. This gives you the amount of time the
engine can hover when it starts with a full load of fuel.
For a large modern turbofan engine hovering in place at sea level, this number
comes out to a little over 90 minutes. When you add on the extra weight of your
house, it means your flying time will be less than 90 minutes, no matter how
many engines you add. If you limit your horizontal speed to 60 or 70 mph, and
you’re moving farther than 100 miles, then you’ll need to stop for fuel along the
way.*
MOVING IN
When you arrive at your new home—or your old house arrives at its new
location—there’s a huge amount of work left to do. If you’ve brought your entire
house, you may have to dig a foundation,* and if there’s an existing foundation,
you’ll need to connect your house to it and firmly affix it. If there’s already a
house on the foundation you want to use, make sure to remove it before putting
your own house there. Just send someone ahead of you with another set of
engines and have them repeat the steps above on the house at your destination.
Once you reach the point where the house is in the air, turn up the jet engines to
full and jump out. After that, you can stop worrying about it; it’s somebody
else’s problem now.
After moving in, you may need to set up the utilities, like heat, water, and
power.* If you’re feeling particularly civic-minded or excited about becoming
part of your new community, you may want to introduce yourself to your new
neighbors.
UNPACKING
If you’ve brought your possessions in moving boxes—or packed them up to
secure them during flight—then you’ll have a lot of work to do. You’ll need to
set up your furniture so you have a place to put your stuff, then unpack the boxes
full of stuff and figure out where everything goes, which may involve a lot of
trial and error.
If unpacking seems too daunting, you can adopt a strategy that has probably
been popular as long as humans have been moving their homes from one place
to another: clear enough room to put your mattress on the floor, unpack the one
box that has your toothbrush and phone charger, and worry about the rest in the
morning.

CHAPTER 8
How to Keep Your House from Moving
Once you’re settled in to your house, you generally want it to stay where it is.
If you’re worried that the house will blow away, or that some prankster will
attach jet engines and send it blasting off into the distance, you can attach it to its
foundation with hurricane ties. The foundation can also be anchored to the
bedrock below using long metal piles.
But what if the bedrock itself moves?
Tectonic plates are in constant motion. Much of North America is moving
west, relative to the rest of the Earth, at about an inch per year. It seems obvious
that property lines must move with the crust, since the alternative would be
ridiculous—an inch of plate movement per year is enough that within just a
decade or two, you could lose your garden on one side of your house while
taking ownership of your neighbor’s on the other.
Rather than being defined by coordinates, geographic boundaries are generally
anchored to the ground. As a general rule, the final legal authority on the exact
location of a boundary is typically not a set of coordinates or the text of the
agreement creating the border—it’s the markers left by the original survey based
on that agreement, along with documentation created by the surveyors that can
be used to reconstruct the location of each marker if it’s moved or destroyed.
The International Boundary Commission, the body in charge of managing the
US-Canada border, periodically publishes updated coordinates for the border,
but their publications don’t change where the border is—they just provide
everyone with better information about it. The actual border is defined by
“boundary monuments”—usually granite obelisks and steel pipes driven into the
ground—along with photos and surveying information. If the land moves, the
borders move with it, and the coordinates need to be updated.
To reduce the need for these updates, different countries and organizations
often use slightly different latitude and longitude grids—geodetic datums—
which are anchored to a particular tectonic plate. These grids move with the
plate, and may differ from one another by several meters or more. Thanks to
these different grids, no latitude/longitude coordinates are ever really precise and
unambiguous without lots of information about the datum they’re in. If you think
that sounds like a huge headache for anyone who has to deal with precise
coordinates, you’re right.
By using a continent-specific grid, governments and property owners can
partly mitigate the problem of the ground drifting out from under the grid—but
that doesn’t solve it completely, because sometimes one part of a continent is
moving relative to another.
If your house is located on a plate boundary like the San Andreas fault, one
part of your yard might be moving past the other at over an inch per year, and
boundary monuments might start to disagree. Does your yard gradually split into
two pieces? Could your house drift off your lot completely?
The 1964 Alaska earthquake shifted much of the city of Anchorage sideways
by roughly 15 feet. To deal with the resulting land-ownership questions, the state
passed a law in 1966 allowing all property lines to be resurveyed to match the
new location of the ground. California passed a similar law, the Cullen
Earthquake Act, in 1972, which let property owners ask courts to redraw lines in
a way that protected the interests of all those involved.
If you live in Alaska or California, at least, it might seem like these rules
would keep your neighbor from gradually taking ownership of parts of your
house. But there’s a catch: courts have ruled that these laws apply only to sudden
movements, not gradual ones.
In the 1950s, road construction in the coastal town of Rancho Palos Verdes,
California, caused an entire neighborhood to begin gradually migrating downhill
in a creeping slow-motion landslide. By the end of the 20th century, the
neighborhood had moved several hundred feet, putting some houses on property
claimed by the city. The city told the homeowners to leave, but some occupants,
including homeowner Andrea Joannou, took the city to court to ask that the
property lines be redrawn. In 2013, in the case Joannou v. City of Rancho Palos
Verdes, the courts ruled in favor of the city, determining that since the land
movement was not caused by a sudden and unforeseen event, the homeowners
could have taken steps to respond—presumably, steps such as anchoring the
homes to bedrock, or having them moved back up the hill every few years.
If the bedrock itself is moving, you could find yourself in unsettled legal
territory. If there are established boundary monuments nearby, and they moved
along with you, then you can argue that your property is anchored to those
monuments. After all, they’re the final authority on property lines. But if the
boundary monuments are far away or have gone missing—as is often the case—
then your property may be defined only by coordinates relative to some larger
grid, and you might conceivably find that your plot of land has drifted into
someone else’s possession.
In that case, your best approach might be to try to buy the land on the far side
of the neighbor’s house. That way, if your neighbor takes possession of part of
your house, you can simultaneously take possession of part of theirs.
But when it comes to schemes to apply property line rules in unusual
circumstances, you may want to be cautious. In their 1991 decision in Theriault
v. Murray, Maine’s Supreme Court said that boundaries are determined “. . . in
descending priority, by monuments, courses, distances, and quantity, unless this
priority produces absurd results” [emphasis added].
If you do end up in court with your neighbor . . .
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CHAPTER 9
How to Build a Lava Moat
There are lots of reasons for wanting a lava moat around your house, some more
practical than others. Perhaps you want to deter burglars, keep ants from getting
inside, or stop neighborhood kids from stealing pies that you leave cooling on
your windowsill. Or maybe you want to give your landscaping more of that
“medieval supervillain” aesthetic and create some excitement for your
neighbors, fire department, and local zoning board.
MAKING LAVA
It’s actually pretty easy to make lava, at least in principle—the ingredients are
just rocks and heat.

Most rocks melt at temperatures between 800°C and 1,200°C. That’s hotter
than a household oven, but achievable using a high-temperature furnace,
charcoal forge, or even a giant magnifying glass.
To provide the actual material for your lava, you could try using whatever
rocks you find lying around, but be careful; some rocks will melt or explode
when heated due to trapped gases. The Syracuse University Lava Project, which
produces artificial lava for both geologic research and art projects, uses billionyear-old basalt from Wisconsin. The basalt formed when the core of the North
American continent developed a crack down the middle and large amounts of
magma bubbled through. The crack eventually healed up, but it left a crescentshaped scar of dense basalt buried beneath the soil of the Midwest.
If all you care about is having a moat that sets things on fire, you don’t
necessarily need to stick with volcanic rocks at all; you could also try using the
sorts of molten glass used in glassblowing, or a metal with a reasonable melting
point, such as copper. Aluminum’s low melting point makes it an appealing
moat material, but it melts at a low enough temperature that it doesn’t really
glow—and it’s not really a lava moat if it’s not glowing ominously.
KEEPING LAVA MOLTEN
Keeping lava molten is difficult because lava constantly radiates energy in the
form of light and infrared radiation. Without a steady supply of heat, the lava
will quickly cool down and solidify. This means you can’t simply melt your
lava, pour it into your moat, and call it a day. To keep it from cooling down and
solidifying, you’ll need to supply a steady flow of heat energy to make up for the
losses.
Your moat is going to need some kind of built-in heating apparatus.
You can think of a lava moat as a long, skinny, high-temperature open-top
furnace. Industrial furnaces of this sort are often gas heated, but there are also
electric versions that use high-temperature heating coils. Gas heating may cost
significantly less, but electric furnaces tend to be simpler and offer more-precise
temperature control. Regardless of the power source, the basic design is the
same: a crucible to hold the lava, a heating coil or hot gas jet to heat the crucible,
and insulation around that.
How hot does our lava need to be? We can pick materials with a low melting
point to reduce energy consumption, but if the temperature is too low, the moat
won’t glow.
For something to glow from heat, its temperature has to be above about
600°C, and if you want a really nice bright orange-yellow color visible in the
daytime, like the kind of lava you see in the movies, you’ll need a temperature
above 1,000°C.
We can use research on real lava flows to estimate how much energy a moat
will radiate when the lava reaches a particular temperature, which tells us how
much energy you’ll need to supply to keep it molten.
The chart above tells us that a 900°C lava pool will radiate roughly 100
kilowatts of heat per square meter. If electricity costs around $0.10 per kilowatt–
hour, then each square meter of a 900°C lava moat will cost at least $10 per hour
if heated electrically. If your moat is a meter wide and encloses an area of one
acre, it will cost roughly $60,000 per day to keep it molten.
A 1-meter-wide moat might seem too narrow to deter human intruders,* since
people can normally hop over a gap of that size without too much trouble.
However, the heat of the lava moat will be dangerous even if they don’t fall in.
Near the surface of the lava, the heat will be intense enough to cause seconddegree burns in less than a second. Even approaching the lava may be difficult.
For someone standing a few meters away, the heat flux would be pretty high—
enough to cause pain in exposed skin within 10 seconds, according to firefighter
safety guidelines.
A 1-meter moat isn’t impenetrable; someone wearing thick clothes and boots
could conceivably jump over the moat without injury, as long as they avoided
falling in and didn’t linger too long on either side.
You could deter moat-jumpers by making the moat wider or the lava hotter.
Both of those options will increase the expense, as shown by this approximate
price table:
COOLING
So far, we’ve only discussed the cost of heating the lava. But if you’re going to
live in the middle of this lava moat, you’ll need to worry about cooling the house
as well. Even with a sizable gap between the moat and the house, the lava’s heat
radiation will eventually make things uncomfortably hot in the house. If the side
of the house is 10 meters from the moat, and you stand near a window, the heat
radiation will exceed firefighter thermal exposure limits.
You can reduce the amount of thermal radiation reaching the house by
recessing the moat into the ground, so more of the heat radiates upward. But this
will only partially solve the problem; the ground around the moat will still be
pretty hot, and radiate heat toward you. If there’s a breeze, it will carry a stream
of hot air downwind from the lava—and that’s an inherent problem with lava
moats: no matter which way the wind is blowing from, you’re always
downwind.
Fortunately, cooling your house is easier than heating your moat. If you have
a source of cold water, like a nearby spring or river, you could run the water
through your walls to carry away excess heat. Water’s huge heat-storage
capacity means that it can be used to remove a lot of heat with only minor
pumping costs. This strategy has been used by tech companies to cool server
rooms: Google, for example, has a data center on the coast of Finland cooled by
seawater.
You may also want a source of ventilation from outside the moat, especially if
your particular lava mix is prone to giving off toxic gas. Luckily, the heat of the
lava can help you out here—if you install ventilation tunnels under the moat, the
rising air from the lava will tend to suck air in through the low-level tunnels.
This “natural draft” effect is used in industrial cooling towers like those over
nuclear reactors and may reduce the need for fans to bring in cold air.
But be careful—if your water-cooling system takes in water from the ocean,
you may find it unexpectedly clogged; nuclear reactors have sometimes gone
into emergency shutdown when their intakes are blocked by swarms of jellyfish.
The jellyfish may point to a deeper problem with lava moats. Installing a lava
moat provides additional protection, but the moat requires additional
infrastructure, which creates its own vulnerabilities.
The jellyfish-clogged water intakes are bad enough, but from a supervillain
point of view, perhaps you should be even more worried about the network of air
ducts beneath your house. Because if there’s one thing we’ve all learned from
action movies . . .
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CHAPTER 10
How to Throw Things
According to a well-known legend, George Washington threw a silver dollar
over a big river.
Like many anecdotes about Washington, this claim didn’t spread until after
his death, and the details are hard to pin down. Sometimes it’s a silver dollar,
sometimes it’s a rock. Sometimes the river is the Rappahannock, sometimes it’s
the much wider Potomac. All we can say for sure is that people really liked
telling stories about Washington, and apparently “throwing something over a
river for no reason” was seen as a heroic deed.

It’s not clear why throwing a silver dollar over a river is a good qualification
to be president, but people seemed impressed by it. It’s a shame that the story
didn’t become popular until after his death, because the campaign ads would
have been pretty good.
Which objects could Washington have thrown over which rivers? How would
he stack up against other presidents, and other non-presidents?
Let’s look at a very abstract representation of what happens when a person
throws something:
1. Person has the object
2. ???
3. The object is flying away
Oddly, even without knowing what happens in step 2, it turns out we can
come up with a pretty good guess about how far someone can throw an object by
looking at the constraints placed on them by physics.
Human bodies are limited in size. Whatever the thrower does to the projectile
has to happen within a small region of space around their body.
In order to throw something, a person needs to accelerate it using their
muscles, and human bodies can only exert so much muscle power at once.
Across a variety of sports, from rowing to cycling to sprinting, the power output
that top athletes can deliver to an object over a short burst—such as a rowing
stroke—is usually limited to around 20 watts per kilogram of body weight. This
suggests an athlete who weighs 60 kilograms might have 1,200 watts of power
available for throwing.
Let’s assume the athlete “throws with their whole body,” delivering that full
power output to the ball over the short distance before it leaves their grasp:
Under these assumptions, we can use the equations of motion under constant
power* to determine the ball’s final speed:
If we plug in the average weight of an MLB baseball pitcher (208 lb) and the
mass of a baseball (5⅛ oz), and we assume the throw motion covers a span
similar to their height (6 feet 2 inches), we should be able to figure out a very
rough estimate for a pitcher’s fastball speed:
Ninety-four mph is almost exactly the average speed for a four-seam fastball!
Not bad for a formula that knows nothing about the pitcher.
If we put in numbers for a quarterback and a football, we get 67 mph. That’s a
little faster than actual football passes, which top out around 60 mph, but it’s not
far off.
Sadly, the precision of our answer is probably just coincidence, since this
model has a problem.
According to our equation, extremely light balls can be thrown arbitrarily fast:
a baseball that weighed half an ounce could be thrown at 200 mph! In reality, a
baseball pitcher can’t deliver all their power to the ball—they need to accelerate
parts of their hand and arm to high speeds along with it.
To account for the hand speed limit, we can add a small “fudge factor,”
tweaking the formula by adding a little bit of weight to the ball—equal to
1/1000th of the player’s body weight—to represent the weight of the fastest part
of their hand. This places an upper limit on throwing speed for lightweight
objects, which is consistent with reality, without distorting the results for heavier
objects too much.*
We can combine this with an approximate equation for the distance a
projectile will fly through the air* to produce a unified theory of people
throwing stuff really far:
Power output: 20 W/kg for a trained athlete, 10 W/kg for a normal human
v = throw speed, vt = terminal velocity
This model isn’t perfect. It’s an unwieldy set of equations, and it’s based on
just a few input variables and extremely simple assumptions, so it can’t be more
than an approximation. We could make it much more accurate by putting in a
more specific model of throwing mechanics, or more accurate data about
pitchers. But if we make the model more specific, it becomes narrower in what
we can apply it to. What’s really fun is how broad it is. We can plug in anything.
Sure, we can use it to figure out how far a quarterback can throw a football.
The longest NFL passes tend to travel 60-something yards through the air, and
our equation gives a result that’s pretty close.
(NFL quarterback, football) → 73 yards
But we can also use it to figure out how far a quarterback can throw other
objects. Let’s try an 11½-lb Vitamix 750 blender:
(NFL quarterback, 11½-lb blender) → 18 yards
All we need is a rough idea of the blender’s weight, shape, and drag
coefficients.
We’re not limited to quarterbacks, either. We can plug in anyone whose
height and weight we can estimate.
(Former president Barack Obama, olympic javelin) → 97 feet
(Singer Carly Rae Jepsen, microwave oven) → 12 feet
You can play with this calculator at xkcd.com/throw.
Using this formula, along with your height, weight, and level of athleticism,
you can figure out how far you can throw arbitrary objects.
WASHINGTON’S THROW
What does our model say about George Washington’s silver dollar feat?
Washington was famously athletic and liked throwing things—he reportedly
threw a rock to the top of Virginia’s Natural Bridge from the river below—so
we’ll give him a power ratio of 15 W/kg. That puts him halfway between a
normal person and a trained elite athlete.
The drag coefficient of a silver dollar varies depending on how it’s thrown. If
it’s tumbling, it has a much higher drag coefficient, but if it’s spinning like a
Frisbee, it flies more efficiently.
(George Washington, silver dollar (tumbling)) → 176 feet
(George Washington, silver dollar (spinning)) → 467 feet
The Rappahannock river is only 372 feet wide at the place where Washington
supposedly threw it. With the right spin, it’s possible he could have made the
throw! (The Potomac, at over 1,800 feet, is too wide.) And, confirming this,
many people have successfully recreated the throw. In 1936, retired pitcher
Walter Johnson successfully threw a silver dollar 386 feet over the
Rappahannock. A day earlier, first baseman Lou Gehrig threw a silver dollar
over a 400-foot-wide stretch of the Hudson.
Our model is just an approximation. But the answers it gives don’t seem too
far from reality, and it’s remarkable that we can get even vaguely realistic
answers about a complex physical action like “throwing” using so few pieces of
elementary physics.
At least, the answers are realistic in some sense, if not in others.
(Carly Rae Jepsen, George Washington) → 35 inches
CHAPTER 11
How to Play Football
There are lots of games called “football,” connected through a complicated
genealogical tree.
If you’re not sure which version you’re playing, you can try asking the other
players, or watch what people are doing and guess from context.
Most versions of football have a number of elements in common. They
involve two teams of a dozen or so players, one team on each side of a large
field, each trying to get a ball into the goal at the opposing team’s side. They
also almost always feature kicking at some stage of the game, but different
versions allow you to touch the ball with different parts of your body.
There are lots of players on the field, but generally only one of them can have
the ball at a time, so there are plenty of opportunities for you to just run around
on the field without ever having to deal with the ball. You can just do your best
to look busy, and as long as you don’t get near the ball, maybe no one will notice
you.
Eventually, someone may try to give you the ball—this happens a lot if you’re
playing American football and you’re the quarterback. Or you might get bored
with running around and decide to take the ball, either by catching it or—
depending on the rules—grabbing it from someone as they go by.
Once you have the ball, everyone will pay attention to you, and lots of people
will try to take it away. If you aren’t enjoying the pressure, you can hand it off to
a teammate.
If you’re feeling ambitious, you can try to score points yourself. In football, as
in so many sports, the general way to accomplish this is simple: get the ball to
the goal.
THROW THE BALL INTO THE GOAL
In some types of football, you can score points by launching the ball into the
goal from a distance, which you can do by throwing, kicking, or using some
other part of your body.
Throwing or kicking the ball directly into the goal might not be an option. In
some cases, the rules might not allow a goal to be scored this way—in American
football, the quarterback can’t just throw the ball through the goal (although it
must be tempting sometimes.)
If you decide to attempt to throw or kick the ball into the goal, make note of
the distance to the goal and weight of the ball, then turn to chapter 10: How to
Throw Things.
In versions of football where you are allowed to fling the ball directly into the
goal, throwing from a great distance might not be very effective. In association
football, for example, it’s perfectly legal for the goalie to throw the ball into the
opposing team’s goal, but it almost never happens. When the goalie tries to
throw the ball that far, it generally bounces, rolls, and slows down, giving the
opposing goalie plenty of time to catch it.
If you want to try to score a point, but you don’t think you can throw the ball
from where you are, you’ll need to take it to the goal yourself.
TAKE THE BALL TO THE GOAL YOURSELF
Based on the distance alone, walking over to the opposing goal with the ball
should only take you a minute or so, and less if you’re willing to jog:
But be warned: the other players may not cooperate—particularly the ones on
the opposing team.
The other team may try to put players between you and the goal to prevent
you from reaching it. Unless you’re much larger and stronger than the other
players, this will be a problem—and, unfortunately for you, most football teams
are made up of people who are both large and strong. You can try running
around them, but it’s harder than it looks—football players are pretty fast, and
they know sometimes people try tricky stuff like that, so they’re ready for it.
If another team is trying to stop you from getting to the goal, running faster
won’t help. The players weigh as much as you, and there are a lot of them, so
they’ll be able to absorb almost all of your forward momentum. It would take a
huge amount of power to push through them.
One way to get through a wall of opposing players would be to take steps to
increase your weight, speed, and power.
A person on a very large horse has a combined weight roughly equal to that of
an American football team, and the horse’s high speed would give a momentum
advantage, making it easier to shove through the opposing team.
FIFA’s Laws of the Game, the official rules for association football, do not
contain the word “horse,”* so you could try to make an Air Bud argument:
there’s no rule in the books that says you can’t use a horse in football. There are
rules against equipment, but a horse isn’t equipment—it’s a horse.
The referees may not find your argument convincing. If you ride a horse onto
the field, there’s a good chance they’ll try to stop you. Referees are typically
smaller than players, and there aren’t as many of them, but they’ll still add to the
crowd that you have to push through on your way to the goal. They’ll likely also
decide that your goal doesn’t count, but at this point you’ve probably forfeited
that already.
A horse is much bigger than a person, and can certainly knock a handful of
people out of its way. But a larger group of people might present too much of a
barrier for even a large horse to push through.
The climactic battle at the end of the Lord of the Rings movie trilogy showed
horses riding through a seemingly endless sea of orcs, knocking them out of the
way as they went. Would it be possible for a horse to do this without losing
speed?
We can actually answer this question using equations for air resistance—
except with orcs in place of air.
The basic formula for calculating air resistance is the drag equation:
When an object flies through the air, it runs into air molecules and has to push
them out of the way. In a sense, the drag equation can be thought of as
representing the total mass of air that the projectile has to move through, and
how much momentum that air carries:
The main parts of the drag equation can be derived from this diagram.* When
an object goes faster, it collides with more air molecules per second, and those
air molecules are moving faster relative to the object, which is why speed is
squared. If an object’s speed doubles, it will hit twice as much air per second
and the air will be going twice as fast, so the impulse delivered by the air each
second—the force—goes up by a factor of 4.
We can use this equation to calculate how much power an object needs to
exert to overcome this resistance and maintain its speed. Energy is force times
distance, and power is energy per second, so the power the object must exert is
equal to the drag force times the distance it travels each second. Since distance
per second is speed, therefore power equals drag force times speed. We already
multiplied by speed twice to get drag force, and now we need to multiply by
speed again:
That “3” in the exponent tells us that as an object goes faster, the power it has
to exert to overcome drag rises very quickly.
Strangely enough, we can use this same approach to estimate how much
energy a horse would exert while plowing through a crowd of orcs, by treating
the orcs as a uniform gas with very large molecules.
Adapting the equation to the horse-orc geometry gives us this equation for
power:*
Note: We’ve gotten rid of the factor of ½ and the drag coefficient. For a “gas”
made up of individual non-interacting molecules that bounce off the front of a
curved object as it moves, the drag coefficient works out to around 2.
The orcs in the film are probably standing with a density of roughly 1 orc per
square meter. If we assume each orc weighs 200 lb, and the horse is 2½ feet
wide at the chest and galloping at 25 mph, that works out to:
Can a horse sustain a power output of nearly 100 kilowatts? To know that, we
need to know the sustained power output of a horse. Conveniently for us,
“horsepower” already exists as a unit, so the calculation is just a simple unit
conversion:
One hundred thirty horsepower is too much for one horse. A horse can do
more than 1 horsepower of work for a short time—a horsepower is defined by
work done over a long period—but a horse’s maximum short-term output is
more like 10 or 20 horsepower, far short of the 130 needed for the feat in the
movie. To reduce the power required to push through the crowd of orcs, the
horse would need to slow to a trot.
The orc resistance equation also applies to football players, referees, and any
other horde of enemies that you might want to charge through on horseback. If
you’re going to push through a crowd of players on horseback, you’ll need to
slow way down, which will give your opponents a chance to brace against you,
climb onto your horse to overload it, or grab your legs and drag you from the
saddle onto the field where you can be tackled in the traditional manner.
Like any trick play, the horse gambit loses effectiveness if the opposing side
has a chance to prepare for it. Once the opposing players get wind of your plan,
they’ll be able to prepare with anti-horse defensive measures, like long spears
braced in the ground, trenches dug in the field, or strategically placed treats to
distract your mount.
But with only a handful of players on the field, if you aim for an opening in
their defensive line, you might be able to make it through with just a few
collisions. No human runner can catch up to a horse at full gallop, so once you
get past the defenders, you’ll have a clear shot all the way to the goal.

CHAPTER 12
How to Predict the Weather
What will the weather be like tomorrow?
When people talk about the weather in their particular location, they often
repeat an old saying: “If you don’t like the weather in [insert location here], just
wait five minutes.” Like every clever saying, it’s often attributed to Mark Twain.
In this case, he probably did actually say it, but if it turns out he didn’t, you can
just attribute it to Dorothy Parker or Oscar Wilde.
People repeat this quote just about everywhere in the temperate zones,
because weather changes all the time and we’re constantly surprised by it for
some reason.* These changes can be hard to predict, but since weather is
something that everyone has to deal with—we’re all trapped together at the
bottom of this atmosphere—we try anyway.
There are lots of ways to predict weather, some better than others. The best
modern weather prediction involves sophisticated computer models, but let’s
start with a basic, time-honored technique: guessing at random.
This doesn’t work very well at all.
A slightly better method is to make up your prediction by looking at the
average weather for that place at that time of year. This is called climatology
forecasting.
In places where the weather doesn’t change very much, like the tropics, this is
a pretty good method. For example, the average high temperature in Honolulu,
Hawaii in mid-July is 88°F, so we can use that to make a forecast for next July:
Here’s the actual recorded temperature on those days for a recent year—2017
—in Hawaii:
Nice! Our “prediction” holds up pretty well. We nailed the temperature
exactly on 4 of the 7 days, and were never off by more than a degree. Fame and
fortune as a weather forecaster lie in our future.
Now let’s take this great method and apply it to Saint Louis, Missouri in
September. The average high in mid-September is 79°F, so we’ll use that to
make our forecast:
Here’s the actual 2017 temperature on those days:
Yikes. We were way off!
Forecasting based on averages works better in the tropics because there’s less
variation in the weather. In the temperate zones, where St. Louis is located,*
weather is dominated by the movement of big, slow high- and low-pressure
systems, which can lead to heat waves, cold snaps, and lots of complaining.
Overall, guessing based on averages seems like a bad strategy. But before we
move on to good strategies, there’s another bad strategy we might want to
consider: looking at the weather right now and assuming it will never change.
This sounds silly, because weather changes constantly, but it doesn’t change
that fast. If it’s raining now, it’s pretty likely to be raining 30 seconds from now.
If it’s unusually hot right now, there’s a decent chance that it will still be
unusually hot an hour from now. You can use this principle to make a forecast—
just check the weather right now. That’s your forecast. This is called persistence
forecasting.
Over very short time ranges, persistence forecasting works better than
forecasting based on averages, and over very long time ranges, average
forecasting works better. In some areas of the world, where weather patterns
tend to linger for days at a time, persistence forecasting is more useful. In other
areas, the weather one day has almost no connection to what the weather will be
like the next day. In those areas, forecasting based on averages works better.
COMPUTERS
In the years following World War II, at the dawn of the computer era, the
mathematician John von Neumann launched a project to use computers for
weather forecasting. By 1956, he had concluded that forecasting could be
divided up into three domains: the short term, the medium term, and the long
term. He correctly figured out that the approaches needed in all three would be
very different, and that the middle domain—the medium term—would be the
hardest.
The short term covers the next few hours or days. Over this range, predicting
the weather is a matter of getting enough data and then doing lots of math on it.
The atmosphere operates according to relatively well-understood laws of fluid
dynamics. If you can measure the atmosphere’s current state, you can run a
simulation which shows how it will evolve. These simulations will give us pretty
good forecasts over the next few days.
We can improve these forecasts by gathering more information about the state
of the atmosphere, combining feeds from weather balloons, weather stations,
aircraft, and ocean buoys. We can also improve the simulations, using more
computing power to run them at higher and higher resolution.
But when we try to extend the forecast into the range of several weeks, we run
into a problem.
Edward Lorenz, working on computer weather prediction in 1961, noticed that
when he ran two versions of a simulation with a very tiny difference between
them—like adjusting the temperature at one location from 50°F to 50.001°F—
the outcome would be totally different. The disparity wouldn’t be noticeable at
first, but gradually, the small difference would grow and spread outward through
the system. Eventually, the systems would look nothing like each other on the
large scale. He coined the term butterfly effect for this—based on the idea that a
butterfly flapping its wings on one side of the world could eventually change the
course of storms on the other side of the side of the planet. This idea developed
into chaos theory.*
Because weather is a chaotic system, the medium-term forecast—what will
the weather be like a month or a year from now—may to some extent be
fundamentally unknowable. We’ve discovered some slow-moving cycles that
drive seasonal changes, like El Niño and the Pacific Decadal Oscillation, which
give us hints about overall attributes of the next season. But it may never be
possible to predict on May 1 whether it will rain on October 1.
The long-term domain covers a range of decades to centuries, and is what we
now think of as climate change prediction. Over long-time horizons, the chaotic
day-to-day variation averages out, and the climate is dominated by long-term
energy inputs and outputs. It’s probably never possible to make perfect climate
predictions—since the underlying chaos can always throw a wrench into the
system—but we can say with some confidence how things will change, on
average. If the amount of sunlight entering the atmosphere goes up, so will the
average temperature. If the amount of CO2
in the atmosphere goes down, more
infrared radiation escapes the surface, and the temperature goes down. There are
all kinds of complicated feedback loops involved, some of which we don’t yet
fully understand, but the basic behavior of the system is in principle predictable.
Here’s where that leaves our three domains:
Short: fully predictable, with good-enough computer simulations
Long: hard to predict with certainty, but possible on average
Medium: may be literally impossible
People used to complain all the time about weather forecasts being wrong.
They still do, of course, but the complaints may be getting a little less common.
As we improve our computer simulations and our data gathering, our predictions
over the short term—the ones that go into the 5-day weather forecast—are
getting steadily more accurate. By 2015, the 5-day forecasts were as accurate as
3-day forecasts in 1995. In the mid-20th century, forecasts of the weather more
than two or three days away were no better than the forecasts you’d get from the
simple persistence and averaging methods—which don’t take any computers at
all. Now, our best computer models are making weather forecasts that
outperform those simple methods up to 9 or 10 days ahead of time.
In general, over the last half century, weather forecasts have been improving
at a rate of 1 day per decade, which works out to about 1 second per hour.*
Physics calculations suggest that the fundamental limit to our simulation-based
forecasts is probably in the range of a couple of weeks. After two or three weeks,
the inherent chaotic nature of the system renders prediction impossible.
But you don’t necessarily need access to a supercomputer to predict the
weather.
RED SKY AT NIGHT
According to popular lore, you can predict the weather based on sky color. The
saying typically goes, “Red sky at night, sailor’s delight. Red sky at morning,
sailors take warning.”
This saying has been around in various forms for a long time—there’s a
version of it in the Bible.* The reason it’s lasted so long is that it actually works,
at least in certain parts of the world. The red sky method doesn’t have as much
to do with the red clouds themselves as you might think—instead, it’s a way of
using the Sun to do an X-ray of the atmosphere over the horizon, and then using
clouds above you as a screen on which to project the results!

In the temperate zones, weather systems generally move from west to east.
They don’t move too fast—in general, weather moves across the Earth at driving
speed or slower—so a storm system a thousand miles to your west won’t reach
you for a day or so. Because of the curve of the Earth and the haze of the
atmosphere, you can’t see the clouds to your west; if you could, weather
forecasting would be a lot easier.
The “red sky” trick gets around this by using the Sun. Red wavelengths pass
through air more easily than blue ones. When the Sun is setting in the west, its
light passes through hundreds of miles of atmosphere—becoming extremely red
in the process—before hitting the clouds above you. Shorter blue wavelengths
bounce off the air and go off in other directions. This is why the sky is blue—it
reflects blue light. White clouds reflect all colors, so when red light shines on
them, they look red, too.
If there are storm clouds to your west, the red sunlight is stopped before it can
get to you, and the sunset doesn’t look particularly red:
On the other hand, if there’s clear air for hundreds of miles to your east, the
sunlight passes all the way through to reach the sky above you, turning it red. If
there are any clouds overhead, the red light illuminates them, creating a
spectacular sunrise.
When weather moves west to east, a red sky at night means that there are
clouds overhead, but clear skies to the west—which tells you that the weather
will likely be clearing up.
A red sky in the morning, on the other hand, means that there’s clear air to the
east . . . but clouds overhead. That means the clear zone is moving away, and
clouds are moving in.
This saying doesn’t work in the tropics, where prevailing winds tend to move
east to west and are generally more unpredictable. On the other hand, weather in
the tropics is much more stable—excepting the occasional unpredictable cyclone
—so there’s less need for this kind of rule of thumb.
GOLDEN HOUR
The filtering effect of the atmosphere is part of why the time near sunrise and
sunset is referred to as the “golden hour” in photography. The same warmer,
redder light that creates brilliant sunsets makes for good portraits, as well as
good sunset photos.
This means that in temperate zones, you can get a hint of the coming weather
just by looking at the photos being posted online. If you check Facebook in the
evening and see sunset photos with a higher-than-normal number of red and
yellow pixels, and warmly lit selfies getting an unusual number of likes, it
suggests bad weather is leaving the area. Sunrise photos and glowing morning
selfies, on the other hand, may be an ominous sign.
The photo-color forecast may not be as reliable as a supercomputer-simulation
of the atmosphere, but it’s pretty impressive for an ancient method contained in a
catchy rhyme.
If you’re not a sailor, you can tweak the wording as needed.


CHAPTER 13
How to Play Tag
The rules of tag are simple: One player is It, and tries to chase and touch another
player. If It catches someone, that person becomes It.
There are countless variations on the basic rules of tag—there’s even a
parkour-like league called World Chase Tag that hosts competitions in which
athletes chase each other while leaping and diving over obstacles—but the
standard playground version of tag has very few specific rules. It doesn’t require
scores, goals, equipment, or a defined playing area. Playground tag typically
doesn’t even have a defined end. You can’t win at tag; you can only stop
playing.
In theory, in an idealized game of tag—in which some players are faster than
others, and everyone runs at their top speed—the action should eventually reach
a natural equilibrium. If the person who is It is not the slowest player, then they
will catch a slower player, tag them, and no longer be It. But eventually the
slowest player will become It, will be unable to catch and tag another player,
and will remain It forever.
If the game never ends, the non-It players have to keep running. If they stop
to rest, they risk a tortoise-and-the-hare scenario. If you’re a player who’s faster
than It, but you want to sleep eight hours every day, you have to make sure you
get a large enough lead over your opponent that you can rest without them
catching up.
Our model is still highly idealized. In reality, runners don’t just have a “top
speed.” Some people are fast over short distances, while others can maintain a
pace for a long time. Adding this to our simplistic tag model makes it a little
more interesting.
Let’s imagine a game of tag between Usain Bolt—the world’s fastest shortdistance sprinter—and Hicham El Guerrouj, who holds the world record for the
mile run. We’ll assume both runners are in their athletic prime, and use
measurements from their world-record races to model their pace.
Long-distance runners and sprinters rely on different physiological
mechanisms for power. A sprinter relies on anaerobic processes, which provide a
lot of energy over short distances, but after a minute or two exhaust the body’s
energy reserve. Long-distance runners rely on more aerobic, oxygen-consuming
processes, which provide a steadier supply of energy over long distances.
Usain Bolt is the current world record holder in most sprinting events. He’s
the fastest person in the world . . . unless you need to run farther than a few
hundred meters. His time in the 400-meter sprint is good, but more than two
seconds behind the world record.* At distances beyond that, he doesn’t even
match a good high school sprinter. Bolt’s agent told The New Yorker that Bolt
has never run a mile.
Let’s assume the game of tag starts with El Guerrouj as It, although it doesn’t
actually matter who’s It at the start—if Bolt is It, he’ll simply sprint forward and
tag El Guerrouj within the first few seconds.
Bolt, to escape being tagged, would start to run. At first, he would have the
advantage; his sprinting ability would let him quickly put distance between
himself and the slower El Guerrouj. Thirty seconds into the game, as Bolt passed
300 meters, he would be a full 70 meters ahead of his pursuer.
After 30 seconds, however, the gap between them would start to close. A little
over 90 seconds into the game, El Guerrouj would catch up to Bolt just short of
the 700-meter mark and tag him.
Bolt, exhausted, could try to chase him, but would be unable to catch up.
Assuming you’re not a marathon champion yourself, good long-distance
runners will have a huge advantage over you in games of tag. Whether you’re
Usain Bolt, Uwe Boll,* Ugo Boncompagni,* or Usnea barbata,* you won’t be
able to catch a marathon runner once they get up to speed.
If you do find yourself in Bolt’s shoes, facing someone with superior distancerunning skills, are you doomed to be It forever?
Well, maybe.
HOW TO CATCH A LONG-DISTANCE RUNNER
If you can’t catch a runner by running, you can try the more efficient option:
walking.
Walking is slower than running, but it’s substantially more energetically
efficient—it requires less oxygen and fewer calories per mile. This is why a
healthy person might struggle to run a mile, yet be able to walk for several hours
without any serious difficulty. Running puts a higher demand on your aerobic
system; if your body can’t keep up with that demand, you can’t keep running.
Distance runners learn to run in ways that waste as little energy as possible, but
they also condition their cardiovascular system to supply energy at a rate that
can meet the demand of sustained running.
Hikers typically walk the 2,190-mile Appalachian Trail in 5 to 7 months. The
lower number works out to a pace of a little under 15 miles per day, so let’s
assume you can keep up a 15-mile-per-day pace indefinitely.
Yiannis Kouros, a long-distance running champion, once ran 180 miles in a
single 24-hour period. If you were chasing Kouros at a hiker’s pace, he could
spend the first day running 100 miles to get away from you; then he could rest
for another week or so as you caught up. Once you got close, he could run
another hundred miles.
If Kouros wanted to live a normal life—but was determined not to be tagged
—he could buy two or three houses 100 miles or so apart. When you got close to
one of them, he could run to the next one. That way, he could have a week or so
of rest at each house before you caught up and forced him to flee to the next
house.
Hopefully, any family he lives with are also marathon runners—otherwise,
he’ll have to do a lot more work to stay ahead of you.
HOW TO ESCAPE A MARATHON CHAMPION
If you finally manage to sneak up on Kouros and tag him while he’s not paying
attention, you’ll have a new problem: He’s just going to immediately tag you
back. You certainly won’t be able to outrun him.
If you can’t win within the rules, maybe you can bend them slightly. Let’s
suppose you hop on a magic scooter, one which lets you “run” as fast as you
want, and tag Kourous immediately.
Let’s say Kouros, once he becomes your pursuer, refuses to stoop to your
level, and insists on chasing you the old-fashioned way. No matter how far you
go, he’ll keep chasing you—but if you can get really far away, you can give
yourself lots of time to rest and relax.
You can use Google’s walking directions to try to find the two points on Earth
with the longest walking distance between them. The points change over time as
Google updates its maps, but science artist Martin Krzywinski has collected a
list of them. One promising candidate is a trip from Quoin Point, in South
Africa, to Magadan, a city on the eastern coast of Russia.
This route is about 14,000 miles long. It crosses through 16 countries,
involves ferries over a number of rivers and canals,* and makes more than two
dozen total border crossings. All in all, the walking itinerary includes roughly
2,000 individual directions.
The route is hilly—over a hundred kilometers of total elevation change—and
crosses through practically every climate zone, from tropical rain forest to hot
desert to Siberian tundra. It’s hard to say how fast your pursuer will be able to
travel it, but the record time for hiking the Appalachian Trail is currently a little
over 41 days, an average of 53 miles per day. At that pace, the trek between
Quoin Point and Magadan will take about nine months.
You can continue going back and forth indefinitely, uprooting your life every
year or so to move across the world, until your pursuer gives up.
Or you can talk things over. If a game of tag never ends, and someone has to
be It, why not share? Rather than running back and forth across the world, you
could just pick a nice place to live—perhaps some town you’ve found on your
travels. You and your fellow players could move into houses right next to each
other, and trade off It status every day . . .
. . . by sharing a daily high five with your new neighbors.
Maybe there is a way to win tag after all.
CHAPTER 14
How to Ski
Skiing involves strapping long, flat objects to your feet and sliding across a
surface or down a slope. The surface is usually water, either in frozen or liquid
form, but it doesn’t have to be.
You can slide down any slope if it’s steep enough. When an object sits on a
slope, gravity partly pulls it downward and partly pulls it along the slope. An
object starts to slide when the force pulling it along the surface overcomes the
force of friction.
Depending on what material your skis and the surface are made of, you might
not start sliding easily. If the skis are made of rubber, and the surface is cement,
you’ll need quite a steep slope to ski, which is presumably why rubber-oncement skiing is so unpopular.*
For any combination of surface material and ski material, you can use a
simple physics relation to calculate how steep the slope will have to be to slide.
It seems like it might be a hard problem, but thanks to a convenient coincidence,
most of the complicated parts cancel out, and you wind up with this extremely
straightforward equation:
If you want to know the slope angle, you can reverse the equation:
This equation is delightfully uncomplicated, right up there with E=mc
2* and
F=ma. Unlike those more famous equations, it’s only useful for this very specific
problem, but it’s still neat how simple it is.
Here’s a table of coefficients of friction of different ski/surface materials:
Ski material
Surface Rubber Wood Steel
Concrete 0.90 0.62 0.57
Wood 0.80 0.42 0.3
Steel 0.70 0.3 0.74
Rubber 1.15 0.80 0.70
Ice 0.15 0.05 0.03
Here’s a table of coefficients of friction and the corresponding minimum slope
angle you need to start sliding:
0.01/0.6° (bicycle on wheels)*
0.05/3° (teflon on steel, ski sliding on snow)
0.1/6° (diamond on diamond)
0.2/11° (plastic shopping bags on steel)
0.3/17° (steel on wood)
0.4/22° (wood on wood)
0.7/35° (rubber on steel)
0.9/42° (Rubber on concrete)
Wooden skis would work on a 16° steel ramp. If the skis were made of rubber,
a steel ramp would need to be 35° before you could slide. The coefficient of
friction between rubber and concrete is even higher—0.9—and you’d need a
pretty steep slope of about 42° in order to slide down. This also tells you that a
person in rubber-soled sneakers can’t walk up a ramp with a slope steeper than
42°.
In a sense, skiers are really just mountain climbers who are unusually bad at
climbing but make up for it with very good balance.
Ice is slippery compared with most surfaces, and snow—which is really just
fancy ice—is similarly slick. This makes them a good choice for skiing and
similar activities, which is why every sport in the Winter Olympics involves
sliding in some way.
The reasons that ice is slippery are actually a little mysterious. For a long
time, people believed that the pressure from a skate blade melted the surface of
the ice to create a thin, slippery layer of water. Scientists and engineers in the
late 1800s demonstrated that the pressure of an ice skate blade could lower the
melting point of ice from 0°C to −3.5°C. For decades, pressure melting was
accepted as the standard explanation for how ice skates work. For some reason,
no one pointed out that it was possible to skate at temperatures colder than
−3.5°C. The pressure melting theory suggests it should be impossible, but ice
skaters do it all the time.
The actual explanation for why ice is slippery is, surprisingly, still the subject
of ongoing physics research. The general explanation seems to be that there’s a
layer of liquid water on the surface of ice because the water molecules aren’t
firmly locked into the ice crystal lattice. In this way, an ice cube is sort of like a
piece of cloth with fraying edges. In the middle of the cloth, threads are locked
into a well-organized form, but on the edges, they’re less constrained and more
likely to come loose and move around. In the same way, water molecules near
the edge of a piece of ice come loose and move around, creating a thin layer of
water. However, the properties of this water layer and how a skate interacts with
it aren’t fully understood.
Given how much time modern physics spends on deep and abstract mysteries
like searching for gravitational waves or the Higgs boson, it can be surprising
how many basic everyday phenomena aren’t well understood. In addition to ice
skates, physicists don’t really understand what causes electric charges to build
up in thunderstorms, why sand in an hourglass flows at the speed it does, or why
your hair gets a static charge when you rub it with a balloon. Fortunately, skiers
and skaters can slide on snow and ice without waiting for physicists to finish
figuring things out.
Snow is already pretty slippery, but to gain a little extra slickness, skiers add a
layer of wax to their skis. The wax serves as a semiliquid layer, keeping sharp
ice crystals from digging into the hard material of the skis and slowing them
down.
Waxed skis on snow have a coefficient of friction of about 0.1, which drops to
0.05 once the skis start moving.* This means that you need a slope of 5° to start
sliding under your own weight, but once you get moving, you only need a slope
of about 3° in order to keep going.
Once you’re sliding down a slope, you’ll continue accelerating until you either
run out of snow or you reach a speed at which air resistance is pulling backward
harder than gravity is pulling you forward. Since air resistance doesn’t really
start to kick in until higher speeds, even a gentle slope can let a skier or sledder
go pretty fast if it’s long enough. The theoretical top speed of a skier or sledder
on a 5° slope of unlimited length is around 30 miles per hour—45 if they’re
particularly aerodynamic. On a 25° slope, speeds of over 100 mph should be
possible for an aerodynamic skier or sledder.
The world record for top speed achieved on skis is around 155 mph, but
people don’t keep close track of that record, because it turns out not to be a
particularly interesting boundary to push. The way to reach higher speed is
simply to find a longer, steeper slope. If you keep doing that, skiing gradually
morphs into skydiving—only an even more dangerous version of skydiving,
since instead of falling through open air, participants are skimming across
ground. Obstacles are very hard to avoid when skiing at 155 mph, and even if
you find what seems like a smooth slope, a small bump or gentle turn could be
instantly fatal.
When a competitor’s score in a sport is strongly correlated with their odds of
dying, it creates obvious problems for the sport. Speed skiing was briefly
featured at the 1992 Olympics, but, after a number of deadly accidents, has been
mostly abandoned at the competitive level.
WHEN YOU REACH THE BOTTOM
If you’re skiing down a slope, eventually you’ll reach a point where you can’t go
forward any more. This can happen for a few reasons:
There are trees, rocks, or hills in the way
You reached the bottom of the mountain
There’s no more snow
If you’re having fun and don’t want to stop skiing, you have a few options.
If there are trees in the way, you can try removing them; for more on how to
do this, turn to chapter 25: How to Decorate a Tree. If there are rocks in the way,
you can check chapter 10: How to Throw Things for advice on whether you can
move them. If you’ve reached the bottom of the mountain, you can try
continuing to accelerate yourself forward; you may find some helpful advice in
chapter 26: How to Get Somewhere Fast or chapter 13: How to Play Tag. If you
want to continue downhill even though there’s no more hill, turn to chapter 3:
How to Dig a Hole.
If you’ve run out of snow, read on.
WHAT TO DO IF YOU RUN OUT OF SNOW
From our discussion of friction, we know skis don’t work very well on most
non-snow surfaces. There are some artificial ski slopes that use special lowfriction polymers, with a bristly hairbrush-like texture that provides some
softness and lets the skis dig in when turning. There are also special skis
designed for use on grass and other surfaces, but they use wheels or treads rather
than sliding.
If you want to keep skiing on snow, but there’s no more snow to slide on,
you’ll have to make some yourself.
About 90 percent of American ski resorts use artificial snow to ensure that ski
slopes are covered as soon as it’s cold enough for snow to stick, and to keep
them covered for the whole ski season even if the weather doesn’t cooperate.
The artificial snow also helps to replenish snow lost throughout the season due
to melting and erosion from skiers.
Snow machines make artificial snow by using compressed air and water to
create a stream of tiny ice crystals, and then misting the ice crystals with more
water droplets as they float in the air. As the mist drifts down to the ground, the
water droplets freeze onto the ice crystals to form snowflakes.
The snowflakes formed in this way are more compact and misshapen than the
delicate shape of natural snowflakes. Natural snowflakes have much more time
to grow slowly in a cloud, one water molecule at a time, which allows intricate
and symmetrical shapes to form. Artificial snow forms quickly, in the short time
it takes water to descend from the nozzle to the ground, from a handful of drops
clumsily jumbled together.
Suppose you need a 5-foot-wide path to ski on, and you’re going to descend at
a speed of 20 mph. Natural snow might be 10 percent water and 90 percent air
by volume, although this ratio varies quite a bit depending on how light and
fluffy the snow is. For simplicity’s sake, let’s also assume you want about 8
inches of somewhat heavy snow to ski on, with snow that’s as 1/8 as dense as
water, equivalent in mass to a layer of water an inch thick. The total amount of
water you’ll need is therefore:
Skiing the length of a football field will require a thousand gallons of water,
along with the equipment to turn it to snow.
You’ll have a hard time finding equipment that can produce snow fast enough
for you. The biggest snowmaking machines might produce snow at rates of 100
cubic meters per hour. That’s just 10 percent of what you need, so you may need
a lot of them.
Snow from typical snowmaking equipment needs a lot of time to drift down to
the ground, which means you’ll have to produce the snow far ahead of your
current position to give it time to settle, and the movement of air currents may
make it hard to concentrate enough of it along a narrow path.
The long, slow descent is necessary because it takes a long time for the water
droplets to lose heat to the air through evaporation to attach to the ice crystals.
There are ways to cool the water droplets down more quickly—but they have
some drawbacks.
If you inject low-temperature substances like liquid nitrogen into the air/water
stream, they can reduce the temperature and cause almost-instant freezing. These
techniques can produce snow quickly, and are used by some snowmaking
companies for special events in areas where the air temperature is too high for
normal artificial snow to be produced. Cryogenic freezing techniques are
generally not used by ski resorts—it’s far too expensive and energy intensive to
freeze water this way compared to letting it freeze on its own in the air.
For your small, very narrow ski slope, liquid nitrogen just might be
affordable. If you buy the liquid nitrogen in the form of small tanks, your ride
could cost $50 per second, but industrial suppliers can get you a much better
price if you buy in bulk.
You don’t have to use liquid nitrogen—you could also try other cryogenic
gases. Liquid oxygen is similar to liquid nitrogen and just as easy to produce,
and could in theory be used for snowmaking. However, this is not
recommended. Liquid nitrogen is a popular cryogenic fluid in part because it’s
so inert and nonreactive. Liquid oxygen is neither of those things.
MAKE THE PROCESS MORE EFFICIENT
You could reduce the snow consumption if you could somehow scoop up the
snow behind you and reuse it, rather than producing more snow as you go.
If you lay down some kind of a tarp under the snow, you can pick the whole
sheet of snow back up and reuse it with minimal losses.
The tighter you make the snow-transfer loop, the less snow you’ll need.
You can even make the loops smaller than your body if you pass the stream of
snow around your legs, rather than over your head . . .

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CHAPTER 15
How to Mail a Package
(from space)
Based on the 2001–2018 average, 1 out of every 1.5 billion humans is in space at
any given time, most of them on board the International Space Station.
ISS crew members ferry packages down from the station by putting them in
the spacecraft carrying crew back to Earth. But if there’s no planned departure
for Earth any time soon—or if NASA gets sick of delivering your internet
shopping returns—you might have to take matters into your own hands.
Getting an object down to Earth from the International Space Station is easy:
you can just toss it out the door and wait. Eventually, it will fall to Earth.
There’s a very small amount of atmosphere at the ISS’s altitude. It’s not
much, but it’s enough to produce a tiny but measurable amount of drag. This
drag sooner or later causes objects to slow down, fall into a lower and lower
orbit, and eventually hit the atmosphere and (usually) burn up. The ISS also feels
this drag; it uses thrusters to compensate, periodically boosting itself up into a
higher orbit to make up for lost altitude. If it didn’t, its orbit would gradually
decay until it fell back to Earth.
Astronauts accidentally deliver packages to Earth this way all the time. While
working on the ISS, spacewalkers have accidentally dropped a variety of random
objects, including a pair of pliers, a camera, a tool bag, and a spatula an
astronaut was using to apply a repair adhesive for testing. Each of these
inadvertently created satellites circled the Earth for a few months or years before
its orbit decayed.
A package you toss out the door will suffer the same fate as all the lost parts,
bags, and random pieces of equipment that have drifted away from the station
over the years: it’ll deorbit and enter the atmosphere.
This shipping method has two big problems: First, your package will burn up
in the atmosphere before it ever reaches the ground. And second, if it does
survive, you’ll have no way to know where it will land. To deliver your package,
you’ll have to solve both these problems.
First, let’s look at how to get your package to the ground intact.
REENTRY HEATING
When stuff enters the atmosphere, it often burns up. This isn’t because of some
weird property of space. It’s because everything in orbit is going so fast. When
objects hit the air at those speeds, the air doesn’t have time to flow out of the
way. It compresses, heats up, turns to plasma, and often melts or vaporizes the
object in the process.
To keep our spacecraft from being destroyed, we attach heat shields to the
front, to absorb the heat from reentry and protect the rest of the craft.* We also
give them special shapes, which helps create a cushion of air between the shock
wave and the surface of the spacecraft, keeping the hottest plasma from touching
the hull.
The fate of an object hitting the atmosphere depends on its size.
The Earth’s atmosphere weighs as much as a layer of water 10 meters thick.
To figure out whether a meteor is likely to make it through, you can imagine that
it’s literally hitting a 10 meter layer of water. If the object weighs more than the
water it would have to push aside to reach the surface, it will probably make it
through. This works pretty well for a rough approximation!
Very large objects—house-size or larger—have enough inertia to punch
through the atmosphere and hit the ground without losing much speed. These are
the objects that leave craters in the ground.
Small objects—anything from pebble-size to car-size—are too small to smash
through the atmosphere. When they hit it, they heat up until they break apart,
evaporate, or both. Sometimes, pieces of these objects survive entry into the
atmosphere, either because other pieces absorb the heat and shield them, or
because they’re made of a material that can withstand the reentry conditions. But
when they do, they lose their orbital speed and then fall at terminal velocity
straight down to the ground. After the brief pulse of heat during breakup, this
free fall through the cold upper atmosphere takes several minutes, which is why
meteorites are often very cold when they’re found.
These surviving bits of debris hit the ground at relatively low speeds. If they
land in soft dirt or mud, they can splash a little, but they don’t leave much of a
crater. This is why all impact craters on Earth are large: only large, heavy objects
keep their orbital kinetic energy all the way to the ground. There are impact
“craters” a few feet across—barely larger than the objects that made them—and
impact craters a few thousand feet across, but nothing in between.
Without shielding, spacecraft break up in the atmosphere. When large
spacecraft enter the atmosphere without a heat shield, between 10 percent and 40
percent of their mass usually makes it to the surface, and the rest melts or
evaporates. This is why heat shields are so popular.
To protect your package on the way down, you can use a heat shield, too. The
easiest kind is an ablative heat shield, one which burns away as it goes. It’s not
reusable, like the heat-resistant tiles on the Space Shuttle, but it’s simpler and
can handle a wider range of conditions. Then, you just need to shape the capsule
so that it points in the right direction—heat shield in front, package in back—and
send it on its way.
You may also want to add a parachute, for the final drop, but if your package
is something lightweight or durable, like socks, paper towels, or a letter, it might
be able to survive the final terminal velocity fall relatively undamaged.
Every human-built object which has been designed to survive reentry has used
a curved protective heat shield—with a few exceptions.
THE APOLLO SUITCASES
The Apollo program sent seven teams of astronauts to land on the Moon. Each
crew carried, among other things, a suitcase-size “experiments package” which
would be left on the Moon’s surface to take measurements and transmit
information to Earth. Six of the seven were powered by radioactivity from
plutonium. (The first experiments package, on Apollo 11, was simpler. It had
solar power for its electronics, but still used plutonium heaters to keep it warm.)
Six of the Apollo teams landed on the Moon and deployed their suitcases. One
of them, Apollo 13, famously did not. After part of their spaceship exploded,*
they aborted the mission and flew back to Earth. Everyone was ok, it was very
heroic, etc. But let’s talk about that suitcase.
Since the astronauts didn’t make it to the Moon, they couldn’t leave the
plutonium-filled suitcase there, and it came back with them to Earth. That
created a problem.
Only the command module, with the astronauts inside, was designed to safely
return to the Earth’s surface. The other parts of the spacecraft, including the
lunar lander, were designed to burn up in the atmosphere. The command module
only had enough room for the astronauts and their samples. The suitcase—and
the plutonium core, which was stored separately—would have to stay behind in
the doomed lander. But if the container holding the plutonium broke apart, it
would scatter the radioactive material into the atmosphere.*
Luckily, the engineers behind the suitcase had anticipated this possibility. The
plutonium was contained within a high-strength cask, about the size and shape of
a small fire extinguisher, shielded by layers of graphite, beryllium, and titanium.
The protective shell would allow it to survive reentry, even as the rest of the
discarded lunar module broke apart violently around it.
When the Apollo astronauts climbed into the command module as they
approached Earth, they left the suitcase behind in the lunar module; then they
fired the lunar module’s engines to divert it to the area over the Tonga Trench,
one of the deepest parts of the Pacific—so the cask would fall into the sea and
sink to the bottom. In the decades since, no excess radioactivity was ever
detected, which means the protective shell did its job. The cask of plutonium lies
on the floor of the Pacific to this day. The plutonium is about half-decayed by
now, but it’s still producing over 800 watts of heat as of 2019. Maybe some
deep-sea critter looking for warmth is cuddled up to it right now.
SEND A LETTER
One of the best ways to get around the engineering challenges of reentry might
be to ditch the heat shield entirely in favor of a simpler solution: a manila
envelope.
Lightweight objects that experience more drag start slowing down at a higher
altitude, where the air density is lower. Since the air is so thin, it doesn’t heat the
object as efficiently, and although the reentry takes longer, peak temperatures
can be much lower. In fact, calculations by Justin Atchison and Mason Peck
have shown that an object shaped like a sheet of paper, curved to fall flat side
first, could in theory enter the atmosphere “softly” without ever reaching
especially high temperatures.
If you print your message on a sheet of baking parchment paper, aluminum
foil, or some other thin and lightweight material which can survive being
warmed up, you might just be able to toss it out the door as is. As long as it’s
shaped right, it could make it to the ground intact. In fact, a team of Japanese
researchers planned to try this by launching paper airplanes from the ISS. They
designed the planes to survive the heat and pressure of reentry, but, sadly, the
project never went through.
A package tossed by hand from the ISS will descend gradually over the course
of many orbits, with little control over the eventual landing point. Controlling
where the package will land is much harder than simply delivering it to Earth.
Returning spacecraft generally try to control where they land. Some do this
with more precision than others. SpaceX’s spent rocket boosters can guide
themselves precisely enough to land directly on a target on the deck of a boat,
while the older Apollo and Soyuz spacecraft have generally missed their targets
by a few miles.* Spacecraft undergoing uncontrolled reentry—like your package
—can miss their intended landing site by hundreds or thousands of miles.
You can improve the precision of your package delivery by throwing the
package really hard. A fast throw can get the package down into the atmosphere
more directly, without a long delay as atmospheric drag causes its orbit to slowly
decay in a hard-to-predict way. Surprisingly, the way to do this isn’t to throw the
package downward, toward Earth. Instead, you should throw it backward. If you
throw it downward, it will still have enough forward speed to stay in orbit—it
will just be a slightly different orbit. You want it to lose speed instead.
The faster you throw the package, the more precise its landing. The ISS is
traveling at almost 8 kilometers per second, but luckily, you don’t need to throw
your package that fast. Shaving off just 100 meters per second from the orbital
speed at the ISS’s altitude is enough to deliver your package to the atmosphere.
Unfortunately, throwing something at 100 m/s is difficult. Even the fastest
pitchers don’t break 50 m/s. Golf balls, on the other hand, travel fast enough. A
golfer floating next to the ISS could conceivably hit a golf ball out of orbit in a
single stroke. If your package is the size of a golf ball, you can try that delivery
method.
If you launch the package at 100 m/s, it will enter the atmosphere traveling at
a downward angle of about 1°, which will give you a debris footprint—the area
where your package might land—over 2,000 miles long. If you’re aiming for St.
Louis, it could land anywhere between Montana and South Carolina. If you can
throw it harder—250 or 300 m/s—you can enter the atmosphere at a
proportionally steeper angle and cut the debris footprint down to a few hundred
miles. However, no matter how fast and precise your throw, the randomness of
turbulence and wind will keep you from hitting a target with a precision of better
than a few miles.
MIR
In March of 2001, the space station Mir was about to reenter the atmosphere.
Most of it was expected to burn up, but some of the larger modules had a chance
of making it to the surface. The Russian Mission Control planners tried to time
its reentry so it would come down over an uninhabited region of the Pacific, but
no one knew exactly where it would land.
Capitalizing on this, Taco Bell came up with a unique promotion: they floated
a giant sheet on the Pacific with a bull’s-eye painted on it, and offered a free taco
to everyone in America if any piece of Mir hit the target.
Sadly, no debris ultimately hit the bulls-eye.* Most of the larger pieces hit the
surface of the ocean in the vicinity of 40°S 160°W—the “spaceship graveyard,”
a region far from land where the wreckage of over 100 spacecraft has splashed
down—and sunk to the bottom.
Despite the claims of many eBay auctions, no confirmed Mir debris was ever
recovered. If you do find some, you could always try bringing it to Taco Bell
headquarters in Irvine, California. Maybe they’ll let you exchange it for a taco.
ADDRESSING
You may not be able to aim your package very carefully, but don’t despair—that
doesn’t mean it can’t be delivered! You just need to figure out what address to
write on it. But, as the US government learned in the 1960s, figuring out what to
write on space packages can be tricky.
The first US spy satellites used film cameras. After they had taken their
photos, the capsules containing the film were dropped back to Earth. If all went
well, they would be tracked on the way down, and an Air Force aircraft would
literally catch them out of the air using a long hook.
Things didn’t always work as planned. Several capsules returned to Earth
uncontrolled; one, which came down in the Arctic near Svalbard, was never
found. In early 1964, a Corona reconnaissance satellite—after taking a few
hundred photos—broke down in orbit, stopped responding, and headed toward
an uncontrolled reentry. Government officials watched anxiously, trying to
determine where it would enter the atmosphere. Eventually, it became clear that
it was going to land somewhere in the vicinity of Venezuela.
Observers in the area were told to watch the skies, and on May 26, 1964,
debris was seen streaking over the Venezuelan coast.
The officials thought it had probably landed in the ocean, but it had in fact
fallen on the border between Venezuela and Colombia. It was found by some
farmers, who took it apart, removed the gold discs they found inside,* and tried
to put the rest of it up for sale. A farmer used the parachute lines to make a
harness for his horses. When no one wanted to buy it, the capsule was handed
over to Venezuelan authorities, who contacted the United States.
Up until 1964, the returning capsules were labeled UNITED STATES and
SECRET in threatening letters, intended to dissuade people from opening them
and accessing their highly classified cargo. After the 1964 incident, the United
States changed their labeling strategy. Instead of a stern warning, they simply
stamped them with a message—in eight languages—promising a reward for
bringing the capsule to the nearest US consulate or embassy.
If you want to maximize the chance that the person who finds your package
helps deliver it to its intended recipient, bribery might be the way to go.

CHAPTER 16
How to Power Your House
(on Earth)
You’ve got a home full of stuff that needs to be plugged in. How do you power
your house?
A typical American household consumes about a kilowatt of power averaged
over the year. At 2018 electricity rates, that works out to $1,100 per year. Could
your land offer a cheaper alternative?
Let’s take a look at some of the different sources you might tap into, using a
typical US home as an example.
A median newly built single-family home in the United States sits on a 0.2
acre lot (800 square meters), 25 percent of which is occupied by the house itself.
Let’s assume you live in such a house, and consider what flows of power your
little plot of land gives you access to.
Traditionally, when you owned land, you also owned the column of air above
your land and the dirt under it—as expressed in the maxim Cuius est solum, eius
est usque ad coelum et ad inferos, which means, “The property you own extends
upward to heaven and downward to hell.”

In modern times, your ownership upward may be restricted in various ways—
including local zoning laws, the Federal Aviation Administration, and the Outer
Space Treaty of 1967, which prohibits claims of ownership over outer space.
Your ownership downward may also be limited by the fact that mineral rights
are often sold separately from the land—so you may own the property, but not
everything buried under it.
But assuming you have complete ownership, here are some of the resources
you can expect to find in those three regions:
PART 1: SOLUM
Plants
Plants grow on land, sometimes so enthusiastically that you have to do a lot of
work to stop them.
Plants can be burned for fuel, although it’s not necessarily the cleanest or most
efficient way to produce electricity. If you grow and harvest trees on your land,
you could get a steady supply of power by burning the wood.
Timberland productivity depends on management practices, but the National
Association of Conservation Districts estimates that the supply of wood from a
3,987-acre pine forest with relatively hands-off management can supply 1
megawatt of ongoing electrical power. That means that if you filled your yard
with trees (excluding the 25 percent taken up by your house) then the power you
could produce would be . . .
. . . 38 watts. That’s enough to charge your phone or run a tablet or small
laptop, but not nearly enough to power your whole house.
Other crops might be more efficient—switchgrass, for example, could
produce about a kilowatt per acre in much of the central United States, and
potentially double or triple that in other areas. Unfortunately, even if you planted
it on your roof as well as your yard, that wouldn’t be enough to power your
house.
Water
Water flows over the ground under the influence of gravity, and this
gravitational energy can be harvested by hydroelectric turbines.
The United States averages about 31 inches of rain over its whole land area,
and has an average elevation of 2,500 feet. If the country were a uniform plateau
2,500 feet high, with rain falling across it and spilling over the edges . . .
. . . it would generate a total of 1.7 terawatts of power:
The United States has about 120 million households, so that’s 14 kilowatts per
household!
Unfortunately for your house, that’s a very optimistic assessment. Most of the
United States’ rain falls at lower elevations, and not all of it flows into easily
harnessed streams. The Department of Energy suggests the total available United
States hydropower—which would include building dams on wildlife reserves
and scenic rivers—is 85 gigawatts, 1/20th of that total. That’s just 700 watts per
household.
PART 2: INFERNO
Buried fuel
If your 0.2-acre property represents 1/12,000,000,000th of the United States,
let’s imagine that it contains 1/12,000,000,000th of the United States’ mineable
reserves. Of course, in reality, all those resources are distributed across the
country in small pockets, so you either have much more than that, or much less.
But if they were evenly distributed, here’s what you’d have under your property:
3 barrels of oil. Each barrel of crude oil can provide about 6
gigajoules of power, so 3 barrels is enough to power your house for
about 8 months.
38,000 cubic feet of natural gas, enough to power your home for a
little over 16 months.
19 tons of coal. Coal has an energy density of roughly 20 megajoules
per kilogram, so your 19 tons of coal would be able to power your
house for 12 years.
1½ ounces of uranium, which would power your house for a few
months in a traditional nuclear reactor, or over a decade in an
advanced type of reactor called a “fast neutron reactor.” Fast neutron
reactors are much more efficient, but they’re also much more
expensive to operate, and they involve enriching uranium closer to the
level where it might be useful for nuclear weapons, so they can make
international regulatory agencies nervous.
When you add them all up, those buried fuels represent a few decades worth
of power.
In reality, your plot of land wouldn’t really contain all those fuel deposits—in
all likelihood, it contains none of them. And even if it did, the energy it would
take for one homeowner to dig them up would outweigh the power they’d
generate. Besides, in terms of impact on the Earth’s climate, humans certainly
can’t afford to burn all the fossil fuels hidden in the ground, so maybe it’s just as
well that you leave them.
Geothermal power
The Earth is still cooling off, both from the heat generated when it initially
collapsed into a ball, and from the heat generated by radioactive decay of
potassium, uranium, and thorium deep within the planet. The planet cools by
radiating heat through its surface. In most places, this heat is usually very faint
and hard to detect. In a few places, it’s very hard to ignore.
The heat flow in a typical geologically quiet area might be 50 milliwatts per
square meter, so in principle your property should have access to 40 watts of
heat power indefinitely. Actual geothermal power production involves drilling
wells deep into the Earth, pumping water down, and letting the warm rocks heat
the water. The heat reservoir would be replenished from the surrounding areas,
so you would really be drawing heat from under everyone.
In practice, geothermal power is only practical in geologically active areas
where high temperatures can be found close to the surface. The Geysers, a
sprawling geothermal plant in northern California, produces about 77 kilowatts
of power per acre, so if you happen to live there, you could easily power your
house. In more geologically quiet areas, geothermal power is likely to be—at
best—a source of a little extra hot water.
Tectonic plates
Living on a fault line would have its downsides, but perhaps you could find
ways to take advantage of it. The ground exerts a force over a distance, and force
times distance is energy. An inch of movement a year isn’t much, but that
movement has a virtually infinite amount of force behind it. Could you harness it
to generate electricity?
In theory, yes!
Suppose you built a pair of giant pistons, anchored to a large area of crust on
each side of the fault, and had the pistons compress a reservoir of fluid between
them.
The pressure on the fluid would build up over time, and could be used to drive
a turbine. The maximum theoretical pressure this contraption would generate
would depend on the pressure the piston could tolerate. If the piston material had
a maximum compressive strength of 800 MPa, and the pistons were the width of
your yard and twice as high—so the piston heads had a surface area of 0.4 acres
—then the total theoretical power available would be given by multiplying the
fault movement rate times the area of the piston times the pressure:
This whole system is ridiculous and technically infeasible for a lot of reasons
—and if you tried to build one, you’d probably discover some new ones. But one
reason it’s a ridiculous idea is cost.
The “roots” of the structure that anchored the generator to the crust would
need to extend outward a great distance—otherwise, the crust would simply
crack and new fault lines would form. These “roots” would have a volume
measured in millions of cubic meters. If they were made of steel and extended 5
kilometers in each direction, they would weigh 60 billion tons and cost
something like $40 billion.
Now, $40 billion is a lot of money, but you’d also be saving $1,100 every year
on electricity costs. At that rate, you’d make your money back in . . .
. . . 36 million years.

PART 3: COELUM
The Sun
The average sunlight power falling on a plot of land in the United States varies
by latitude, cloud cover, and time of year, but a typical value is around 200 watts
per square meter. That’s an average over the whole year—the power can reach
1,000 watts per square meter when the Sun is highest in the sky, but clouds,
seasons, and the fact that it’s dark at night bring the average down. (Utilities
usually measure things in terms of kilowatt-hours; in those units, 200 watts is
equivalent to about 5 kWh per day.*)
Modern solar panels convert about 15 percent of the Sun’s energy into
electricity, so if you cover your yard in solar panels, you’ll capture 25 kilowatts
—much more than you need:
You could improve your efficiency by tilting the panels to face the Sun, to
either cover more area—at the expense of your neighbors—or to get the same
amount of power with less ground space . . .
. . . but the effect of this would be relatively small. The limiting factor for
solar power generally isn’t the available area—it’s the cost of the panels. An
acre of solar panels might cost over $2 million in 2019—plus more if you want
to be able to store the power in case the Sun disappears.
At 2019 electricity rates of 13 cents/kWh, a solar panel on our example piece
of land would pay for itself in 14 years—but various tax incentives, and the
opportunities to sell excess power back to the grid, may reduce that “payback
period” significantly. In areas with plenty of Sun and/or generous renewable
energy incentives, new solar panels can pay for themselves within just a few
years.
Wind
The amount of available wind power depends on how windy your area is and
how high above your land you’re willing to build. In general, wind speeds
increase the higher you go, so if you build a taller turbine, you can get more
power from it. The US National Renewable Energy Laboratory has mapped out
the available wind power potential across the United States for turbines of
various heights. The available power is measured in watts per square meter,
which can allow you to calculate the power that will pass through a turbine of a
given size.
An area like St. Louis, with roughly “normal” windiness, has wind power
potential of about 100 W/m2 at 50 meters above the ground, 200 W/m2 at 100
meters, and perhaps 400 W/m2 at 200 meters. Very windy areas, like the Rocky
Mountains, might have power densities more than four times that, while in lesswindy areas like central Georgia and Alabama, the available power might be a
quarter of that.
If your 0.2-acre property is square, then you can fit a wind turbine 28 meters
in diameter—or as wide as 40 meters, if the prevailing winds let you put it
diagonally.

A turbine 28 meters in diameter has an area of 640 m2
. If it’s installed at a
height of 50 meters, where the potential is 100 W/m2
, then the power available
will be 64 kilowatts. Wind turbines aren’t 100 percent efficient; thanks to Betz’s
law, they can never extract more than 60 percent of the energy of the wind
passing through them. In practice—thanks to varying wind speeds and
conversion losses—the actual power captured is closer to 30 percent of the
average available. Still, 30 percent of 64 kilowatts is 19 kilowatts—enough to
power your house and the houses of 18 of your neighbors.
That goodwill might come in handy, since a 28-meter wind turbine 50 meters
off the ground might cause some problems on your street. The bottom of the
blade will be just 36 meters above the ground, so hopefully you don’t have any
unusually tall trees.* And you should probably discourage neighborhood kids
from flying kites.
EPILOGUE: SPACE ITSELF
Some theoretical models of the universe suggest that the quantum fields that
make up space exist in what’s called a “false vacuum.” After the Big Bang, the
fabric of space settled from a high-energy chaotic quantum froth into its current
form. Under these models, the form it settled into isn’t really settled—spacetime itself contains a certain amount of tension, and if perturbed in the right way,
this tension could be released, and space would fall into a fully relaxed, settled
state.
In these models, the false vacuum represents a huge amount of potential
energy in every cubic meter of space. Your yard has lots of easily reachable
space—could you trigger vacuum decay and solve your problems forever?
To answer this question, I contacted astrophysicist and end-of-the-universe
expert Dr. Katie Mack. I asked Dr. Mack how much power would be released if
someone triggered vacuum decay in their yard, and whether it could be
harnessed to power their home. Her response: “Please do not do that.”
“If you could decay the vacuum locally, it would in principle release the
energy of the Higgs field, probably in the form of extremely high energy
radiation,” she said, “but along with that energy you’d get a bubble of true
vacuum expanding at the speed of light, making it impossible to harness any of
the energy before the bubble envelops you. That true vacuum bubble would
incinerate you, then destroy all your particles, and then devour the entire
Universe. And then immediately collapse it.”
Luckily for us, the fact that the universe has existed for this long without
decaying suggests that, even if the false vacuum theories are correct, vacuum
decay isn’t particularly likely any time soon.
“Even though vacuum decay is pretty much inevitable if our current
understanding of particle physics is correct, it’s astronomically unlikely to
happen any time in the next several trillion years. There are better and more
efficient ways to get energy,” added Dr. Mack. “For instance, why not create a
tiny black hole and use the radiation from its Hawking evaporation like a
campfire? Depending on the mass, you could get a nice steady glow that lasts for
years before it spectacularly explodes in its final disintegration!”
That sounds much more practical.
CHAPTER 17
How to Power Your House
(on Mars)
Power is harder to come by on Mars than on Earth.
This is partly for the obvious reason that there’s no electrical grid. But even if
we build one there, the usual sources we draw on for electrical power on Earth
won’t work as well on Mars.
Type of power Does it work on Mars? Reason
Wind power Not really The air is too thin
Solar power Not as well The Sun is farther away
Fossil fuels No No fossils
Geothermal
power
Not as well Not very much geologic activity
Hydropower No No rivers
Nuclear power Not unless you bring your own
fuel
Certain geologic processes needed to concentrate
uranium
Fusion No Doesn’t even work on Earth
But there’s one very unusual potential source of power on Mars. You just
need to be willing to destroy a moon to get it.
You don’t have to feel bad about destroying Mars’s moon Phobos—it’s
already doomed.
Earth’s moon orbits more slowly than Earth spins, so the tidal drag between
Earth and the Moon slows down the Earth and speeds up the Moon. Since the
drag speeds up the Moon, it flings it progressively farther away.* On Mars, the
situation is different: Phobos orbits faster than Mars spins, so tidal drag pulls it
backward, causing it to fall down into a tighter orbit. Over time, Phobos is
moving closer and closer to Mars.
Phobos may not be very heavy compared to other moons—Earth’s moon is 7
million times more massive—but it’s still pretty big by human standards.
Phobos’s mass and speed mean that it carries a huge amount of kinetic energy
as it circles Mars—energy you can potentially tap into.
PHOBOS TETHER
Attaching a tether to Phobos has been proposed before. Normally, the goal of a
Phobos tether proposal is to use Phobos’s position and orbital energy to
efficiently move large amounts of cargo to and from the surface of Mars, which
often involves using one end of the tether as a “skyhook” to grab cargo leaving
Mars’s surface.
But a tether could also be used to extract energy from Phobos directly. If you
attached a 5,820-kilometer tether to the Mars-facing side of Phobos, the end of
the tether would dangle into Mars’s atmosphere. The dangling end would be
moving through Mars’s atmosphere at 530 meters per second (m/s). On Earth,
that would be about 1.5 times the speed of sound, but because Mars’s
atmosphere is mostly carbon dioxide, sound travels more slowly there,* and 530
m/s is 2.3 times the Martian speed of sound.
WIND TURBINES
Wind turbines on the surface of Mars aren’t all that useful because the air is so
thin and slow-moving that it would have trouble even turning a turbine blade.
But the end of the tether would experience wind blowing past at Mach 2.3—and
that’s a different story. The air flowing past the tether would carry around 150
kilowatts of energy per square meter. A turbine 20 meters in diameter would
potentially have 50 megawatts of energy passing through it, enough to power an
entire town.
Wind turbines aren’t normally designed to work at supersonic speeds, because
supersonic winds are rare on Earth outside of meteor impacts, volcanic blasts,
and nuclear shock waves. But there are some turbines designed to attach to
supersonic aircraft or rockets. These turbines are designed to generate power
from the flow of air past the fuselage, in part to power the aircraft’s systems if
the engines die. The supersonic turbines are streamlined and have short, stubby
blades; your Mars turbine will likely need to look more like those than the
typical wind turbine.
Your turbine will be dragged through Mars’s atmosphere by Phobos, which
will sap the moon’s momentum and cause it to spiral inward. The more turbines
you add, the more power you’ll generate and the faster Phobos will descend.
Note: As Phobos gets closer, you’ll need to shorten the tether to keep it from
hitting the ground. Helpfully, the shorter tether won’t need to be as massive to
support its own weight, so over time you’ll be able to support more turbines with
the same amount of tether material.
The total energy available by bringing Phobos down to the top of Mars’s
atmosphere is:
Each American uses, on average, 1.38 kilowatts of electricity, which means
Phobos’s orbit carries enough energy to supply the electricity needs of an
America-size population for almost three millennia. Even if lots of neighbors
move in, there’s plenty of Phobos power to go around.
Space tether projects involve massive amounts of material, and this one will
be no different. Even a small tether from Phobos to Mars will weigh thousands
of tons, and the weight will increase as you add more and larger turbines. The
amount of power produced by a tether turbine is proportional to how much force
the tether exerts on it, so each additional watt of turbine capacity increases the
strain on the tether, and the tether has to be made more massive to support it.
Conversely, we can think of each added kilogram of tether material as
“producing” a certain amount of power.
The weight of the tether, and the efficiency, will depend on the materials you
use and a lot of engineering details, but overall the tether will probably deliver,
at most, 2 watts of power for every kilogram of tether. Since the tether can
produce that energy indefinitely, over a timescale of decades, that 2 watts per
kilogram adds up to far more total energy per kilogram than common fuels like
batteries, oil, or coal.*
The turbines will be inefficient to a degree that’s hard to predict. Since the
airflow is effectively unlimited, your main concern will be reducing the
“wasted” drag on the tether, rather than capturing all the power of the air that
passes through it. It’s possible that alternate turbine designs will prove more
efficient and reliable—you may want to experiment with designs such as
Darrieus turbines, drag-based turbines, or Magnus effect turbines, all of which
find specialty uses here on Earth:
In addition to inefficiencies associated with the turbines, you’ll need to worry
about getting the power from the turbine to your house on the surface, which
will inevitably involve additional losses. Power transmission could involve
anything from beamed microwave power to dropping huge numbers of
rechargeable batteries down to the surface.
When a moon orbits too close to a parent body, tidal stresses can become
strong enough to pull material from the moon’s surface. The distance at which
this happens is called the Roche limit. As Phobos draws closer to Mars, it may
break apart into a debris ring. To keep this from happening, you may need to use
some kind of high-strength net to hold Phobos together, or let it break up into
several smaller moons, each of which can be held together with netting more
easily.
This kind of orbital turbine has a particularly strange feature: the longer you
use it, the more power it provides. Your tether will exert drag on Phobos, which
causes the moon to descend . . . but as it descends, it also speeds up, because
lower orbits are faster. A faster orbit means a faster-moving tether, which means
faster airflow and more turbine power. The tether will produce steadily more
power over the lifetime of Phobos.
WHEN PHOBOS LANDS
Eventually, once drag has withdrawn the full 4×10
22
joules of energy from
Phobos—perhaps millennia in the future, or perhaps in just a few years,
depending on how much power your house uses and whether other colonists are
tapping into the turbines as well—the moon will reach Mars’s atmosphere.
Phobos is similar in size to the rock that collided with Earth at the end of the
Cretaceous—a collision which led to the extinction of most of the dinosaurs.
Phobos’s impact with Mars, whether it is in one piece or several at that point,
will be similarly disruptive. The tether, over thousands of years, will have
consumed gravitational potential energy from Phobos and delivered a total of
4×10
22
joules of it to the planet, while at the same time causing Phobos to
accelerate as it descends. The impact of Phobos with the surface will deliver a
similar amount of energy, but all at once.
Phobos’s impact will leave a long scar girdling Mars, and the collision will
spray a huge volume of debris into space, most of which will fall back down in a
rain of molten rock reaching every part of the surface. As is so often the case, a
“free” source of energy ultimately comes with a terrible long-term cost.
The apocalyptic consequences won’t be all negative. For a brief time, until the
lava rain dies down, some of Mars’s lower valleys may heat up enough so that
liquid water could exist in stable pools on the surface.
If your house happens to be located in one of these valleys, see chapter 2:
How to Throw a Pool Party.

CHAPTER 18
How to Make Friends
If you just start walking, eventually you’ll bump into someone.

This might take a while. You might be lucky and walk right into a crowd of
people, but if you’re in a sparsely inhabited area, it could take weeks. If you start
walking from a random location in an area containing some number of people,
you can calculate the time it will take to run into someone by using the physics
concept of a mean free path:
Some areas certainly make encounters easier than others. Here’s the average
collision interval for a few different regions:
Canada: 2.5 days
France: 2 hours
Delhi: 75 seconds
Paris: 40 seconds
Mercedes-Benz Stadium in Atlanta during a sold-out game: 0.6
seconds
The field during the game: 3 minutes
It’s clear that if you want to physically run into people, you’ll have better luck
in a packed football stadium than in the boreal forests of Canada. And if you do
try the stadium, you’ll have more collisions in the stands than on the field—
although the collisions on the field will probably be more jarring.
But most of the time, random encounters don’t lead to friendships. This is ok.
Occasionally, you may hear someone complain that people walking around in
public need to be shaken up from their routines, that they’re too wrapped up in
their own little worlds. But people have their own lives. They’re not necessarily
looking for a connection at the moment you are.
So if it’s so difficult to connect, how do people ever make friends at all?
We can get some insight into where people meet their friends through surveys.
A Gallup survey of Americans in 1990 asked people where they met most of
their friends. The most popular answer was work, followed by school, church,
neighborhoods, clubs and organizations, and “through other friends.”
A more comprehensive survey by Dr. Reuben J. Thomas, published in
Sociological Perspectives, asked 1,000 US respondents for information about
how they met their two closest friends. The study used the answers to build up a
profile of how friendships form at different ages.
Some sources of friendships remained relatively steady—at all ages, people
made about 20 percent of their new friendships through family, mutual friends,
religious organizations, or encounters in public settings. Other sources of
friendships wax and wane throughout life—at first school dominates, followed
by work. Then, as people approach retirement age, they become more likely to
make friends around the neighborhood and at volunteer organizations.
If nothing else, these studies help answer the question of where people make
friends. Those aren’t necessarily the places that you should go to maximize your
chances of making new friends, but they’re where most friendships begin.
Once you do encounter someone, how do you turn the acquaintanceship into a
friendship?
Here’s the bad news: there’s no magic formula or trick that can make
someone your friend. If there were, that would mean you could apply it to
someone regardless of who they were or how they felt. And if you don’t care
who someone is or how they feel, then you’re not their friend.
Immanuel Kant developed a rule called the “categorical imperative,” which
was at the center of his idea of ethics. He expressed the rule in several different
formulations; the second formulation read, in part, “Act in such a way that you
treat humanity . . . never merely as a means to an end, but always at the same
time as an end.”
In Terry Pratchett’s novel Carpe Jugulum, the character Granny Weatherwax
expressed the principle more succinctly. A young man tried to tell Granny that
the nature of sin was a complicated thing. She said that, no, it was very simple.
“Sin,” she said, “is when you treat people as things.”
Whether or not you buy into the philosophy of the categorical imperative, it’s
good practical advice, because people can tell when they’re being treated as
things. Whatever our faults, humans have countless millennia of experience in
judging the intentions of others—a skill much older and deeper than our ability
to put our feelings into words. We can be shortsighted and confused and make
lots of mistakes, but we can smell disdain and condescension from a mile away.
So while encountering people might be easy, there’s no single set of steps you
can follow to befriend them—because friendship means caring about how people
feel. And there’s no way to decide how they feel yourself, regardless of how
much research or thinking you do. You just have to ask them . . .
. . . a
n
d
l
i
s
t
e
n
t
o
w
h
a
t
t
h
e
y
h
a
v
e
t
o
s
a
y.

CHAPTER 19
How to Send a File
Sending large data files can be difficult.
Modern software systems have moved away from the concept of “files.” They
don’t show you a folder full of image files; they show you a collection of photos.
But files linger on, and will probably continue to do so for decades to come. And
as long as we have files, we’ll need to send them to people.
The simplest, most obvious way to send a file is to pick up the device the file
is stored on, walk over to the intended recipient, and hand it to them.
Carrying computers can be difficult—especially the earlier ones that were the
size of a whole room—so rather than carry the whole computer, you can try
detaching a piece of the computer containing the file. You can then bring this
piece to the other person and let them transfer it to their own device. On a
desktop-style computer, the files may be stored on a hard drive, which can often
be removed without destroying the computer.
On some devices, though, file storage is permanently attached to the
electronics, making removal more challenging.
A more convenient and less destructive solution is removable storage. You
can make a copy of the file, put it on a device, then give the device to the person.
Carrying storage devices around is a surprisingly high-bandwidth way to
transfer information. A suitcase full of MicroSD cards contains many petabytes
of data; if you want to transfer very large amounts of data, mailing boxes of disk
drives will almost always be faster than transferring them over the internet.*
If you want to send data to a specific location that’s too far to walk, but not
convenient to reach by mail—say, a nearby mountaintop—you could try using
some kind of autonomous vehicle to carry it. A delivery drone, for example,
could easily carry a small satchel of SD cards containing terabytes of data.
Quadcopter-style drones don’t work very well over long distances thanks to
the limitations of batteries. If a drone has to carry its own battery, it can only
hover for so long. If it wants to hover longer, it needs to carry a bigger battery,
but that means more weight and faster power consumption. For the same reason
that a house supported by jet engines can only hover for a few hours,* small
coaster-size drones typically have flight times measured in minutes, and the
larger ones used for photography are usually limited to less than an hour in the
air. Even if it flew very fast, a tiny drone carrying a MicroSD card could make it
just a few miles before running out of steam.

You could increase your range by making the drone bigger, adding solar
panels, flying higher, and going faster. Or you could turn to the real masters of
efficient long-distance flight:
Butterflies.
Monarch butterflies travel thousands of miles during their migration across
North America, with some traveling all the way from Canada to Mexico in a
single season. If you look up during the spring or fall on the East Coast of the
United States, you can sometimes spot them gliding by silently overhead, a few
hundred feet above the ground. Their extreme range puts drones—and even
many large aircraft—to shame.
You might think butterflies have an unfair advantage over battery-powered
aerial vehicles, since they can stop to consume nectar and “recharge.” Butterflies
will certainly refuel if they can, but they don’t necessarily need to. Another
butterfly species, the painted lady (Vanessa cardui), is even more impressive: it
flies from Europe to central Africa, a 4,000-kilometer flight that takes it over the
Mediterranean Sea and the Sahara desert.
Butterflies make these journeys powered only by small reserves of stored
lipids. They can fly so much more efficiently than drones in part by soaring—
they seek out thermal columns and mountain waves, then hold their wings steady
and ride the rising air upward like a vulture, hawk, or eagle.
If you want to send your file to someone who lives along the migration route,
could you get a butterfly to carry it for you?
Butterflies can carry weights. Volunteers with groups like Monarch Watch tag
tens of thousands to hundreds of thousands of monarch butterflies each year to
track their migration and monitor their population (which has been in decline in
recent decades). The smaller tags weigh about a milligram, but monarchs have
completed their migration with larger tags that weigh 10 mg or more.
MicroSD cards weigh several hundred milligrams—comparable to the weight
of a butterfly—so butterflies would have a hard time carrying them. But there’s
no reason a storage device can’t be made smaller. MicroSD cards contain
memory chips, and the storage density of these chips might be up to a gigabyte
per square millimeter. Given those sizes, a butterfly could easily carry a tiny
chip with a gigabyte of data. If your file is larger than that, you could break it up
across multiple butterflies, and send multiple copies for redundancy.
When your data finally arrived at its destination, the recipient would have to
check a lot of butterflies to assemble all the pieces of the file. You may need to
develop some kind of touchless butterfly scanner that allows them to scan many
butterflies at once.
You could avoid that problem—and increase your bandwidth dramatically—
by using DNA-based storage. Researchers have stored data by encoding it into a
DNA sample, then sequencing the DNA to recover it. Systems like this can
achieve densities far beyond anything we do with chips—it’s possible to store
and recover hundreds of petabytes of data using a single gram of DNA.
Each year, tens to hundreds of millions of monarch butterflies arrive in
Mexico to spend the winter together in giant colonies in the mountains. If you
tagged ten million of these butterflies with tiny pouches containing 5 mg of
DNA storage each, the total capacity of the butterfly armada would be about 10
zettabytes—10,000,000,000,000,000,000,000 bytes. That’s roughly the total
amount of digital data in existence in the late 2010s.
If the Sun is warm, the winds are favorable, and it’s the right time of year, you
could use butterflies to send someone the entire internet.

CHAPTER 20
How to Charge Your Phone
(when you can’t find an outlet)
The easiest way to charge your phone is to plug it into an outlet. Unfortunately,
they’re not always easy to find when you need them.
Sometimes, when you find an outlet, there’s something already plugged in,
such as someone else’s phone or an unattended piece of equipment. If you carry
a little portable power strip around, you can sometimes unplug the cord for a
moment and plug it into your power strip, then use one of the other outlets—
although you may want to exercise caution while doing this.
If you can’t find an outlet at all, your task becomes a little more difficult.
Instead of being given energy by a friendly wall, you’ll have to take it from the
environment some other way.
Humans extract energy from various natural processes. We burn things for
heat, we collect energy from sunlight, we take advantage of underground heat,
and we harness the movement of wind and water by making them turn the blades
of turbines.*
In theory, all of these techniques can work indoors as well, but they’re a little
more difficult. Sure, you can find light, heat, flowing water, and flammable stuff
in an airport, but usually in much smaller quantities than outside. This is partly
because in an artificial environment, everything is put there by someone. In
physics, energy and work are synonymous. If some human-built contraption is
spewing so much energy into the environment that it’s worth your time to
harvest it, then whoever keeps it running is doing a lot of work for nothing.
Unlike most humans, planets and stars have no problem doing work for free.*
The Sun floods the whole Solar System with light, even the empty parts, and will
continue to do so for billions of years without pause—all you have to do is put
up a solar panel and capture a tiny amount of it. Indoors, there’s less of this
energy for the taking, so it’s not as easy, but it’s still possible. Here are some
ways to capture energy in an airport or a mall:
WATER
There may not be actual rivers in an airport, but there’s often running water.
Water flows out of faucets and fountains, and there’s no reason you can’t use
this water to generate electricity just like a hydroelectric dam does.
You don’t need to build a whole tiny hydroelectric dam.* Since the building’s
water system holds the water in a reservoir and directs it into pipes for you, you
can skip all that and mount a turbine directly on the mouth of the faucet or water
fountain. There are actually companies that manufacture these turbines, either to
run small pieces of equipment attached to pipes, or simply as a replacement for a
pressure relief valve, to extract some usable energy from water. In the late 19th
and early 20th century, many buildings had running water but no electricity, and
these sorts of generators—called “water motors” or “hydro-electric dynamos”—
enjoyed brief popularity.
The amount of power available from a pipe can be surprisingly large. Moving
water carries a lot of energy, and turbines can be very efficient—small turbines
can convert 80 percent of the water’s energy into electricity, and large ones can
achieve even higher efficiencies. A water supply with a pressure of 30 PSI
(pounds of force per square inch) and a flow rate of 4 gallons per minute can
produce over 40 watts of power, which is enough to power several LED bulbs,
charge dozens of phones, or even run a small laptop with multiple browser tabs
open.
In the end, the power you’re using is supplied by the pumps run by the water
company, which create the water pressure in the first place. Eventually, someone
from the airport—or the local water utility—will notice. And even if they don’t,
4 gallons per minute adds up quickly. Whether you’re paying for the water or
not, you have to find somewhere to put it.
Of course, those ramps that connect to the jet slope downward . . .
AIR
Unfortunately, wind power isn’t a great choice for capturing energy indoors.
There’s plenty of air circulating in airports, but “wind” flowing out of a
ventilation duct generally carries a lot less energy than water flowing out of a
faucet and is harder to capture efficiently. A tiny windmill the size of a handheld
portable fan, placed at the exhaust grate of an air conditioning system, could
probably produce about 50 milliwatts of electricity—not even enough to keep a
single phone charged. Even if you covered an entire exhaust vent with fans,
you’d struggle to get even a fraction of the power you could get from a faucet.
This is true outdoors, too—it’s easier to get power from flowing water than
flowing air. The reason we use air at all is because there’s more of it. There’s a
reasonable chance you’re feeling a breeze right now as you read this, but the
odds that you’re standing in a river are slim. The world has more wind than
rivers; the total energy carried by rivers is on the order of a terawatt, while the
total energy carried by wind is closer to a petawatt.
FIRE
ESCALATORS
Escalators give energy to their riders. When you get on an escalator and start
moving upward, the escalator has to consume extra electrical energy to turn the
motors that lift you. This energy is transferred to you in the form of potential
energy. If you turn around and slide down the railing back to the lower level,
you’ll arrive at high speed—having turned the potential energy from the
escalator motors, which you got for free from the escalator, into kinetic energy.
Escalators may be designed to give you potential energy, but with the help of
some simple mechanisms, you can make the escalator give you electrical energy
instead. Really, escalators are just big metal waterfalls, and you can use the
moving stairs to turn an axle, just like a waterfall turning a waterwheel at a mill.
A simple wheel with flat paddles will interlock awkwardly with the escalator.
You can make it work more smoothly by building a wheel with curved paddles
that mesh with the escalator. If you shape the paddles carefully, the wheel can
stay in constant contact with the escalator without sliding.*
The amount of power you can extract from an escalator this way can be
substantial. The mechanical work an escalator does each minute is simple to
calculate—it’s equal to the peak number of passengers per minute times weight
per passenger times the escalator’s height times the acceleration of gravity.
When fully loaded with people, a two-story escalator might easily output 10
kilowatts of mechanical power, much of which you could capture with a welldesigned wheel. That’s not just enough to charge a phone, it’s enough to run an
entire house.
Pro tip: You should probably make the wheel narrow, rather than having it
take up the whole width of the escalator. It’s going to be unsafe either way, but if
it takes up the whole escalator, and someone gets on without noticing, it will
inadvertently turn your contraption into a nightmarish human grinder, which will
likely harm its efficiency.
You should use the “up” escalator rather than the “down” one to turn a paddle
wheel. It’s possible both will work, but the “up” escalator is the one designed to
exert more force when weighed down by people. A “down” escalator has to do
less work when people get on it, since it gets help from gravity, and it may have
problems exerting the extra downhill force needed to turn a wheel. You also may
want to use multiple wheels, which will help spread out the weight on the
escalator.
An escalator waterwheel could extract significant amounts of energy, but that
also means it would cost the escalator owners significant amounts of money. If
you hook up to an escalator and force it to exert an extra 10 kilowatts of power
for 12 hours a day, that could cost the building owners over $400 a month in
electricity bills. Needless to say, they probably won’t be thrilled if they find out.
If you are kicked out of the airport, you should try to take the wheels with
you. In addition to working as escalator waterwheels, they can roll down stairs
without bouncing, which is a pretty cool property.
Comedian Mitch Hedberg once commented that an escalator can never break;
it can only become stairs. Well, an escalator waterwheel generator can never
break . . .
. . . i
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CHAPTER 21
How to Take a Selfie
We sometimes think of our eyes as a pair of cameras, but human visual systems
are so much more sophisticated than any camera—it’s just easy to miss the
complexity because it happens automatically. We look at a scene, get a picture in
our heads, and we don’t realize how much processing, analysis, and interaction
happens to produce that picture.
Cameras generally see all the areas of an image at roughly the same
resolution. If you take a picture of this page with a phone camera, a word in the
center of the picture will be made up of about the same number of pixels as a
word near the edge. But your eyes don’t work that way—they see very different
amounts of detail at the center of your vision compared to the edges. The actual
“pixel grid” of the eye looks very strange:
The reason we don’t notice the wildly varying resolutions is that our brains
are used to it. Our visual systems process the image and give us an overall
impression that what we’re looking at is simply what the scene looks like, the
same thing that would be seen by a camera. This works . . . until we start
comparing our mental picture to what’s produced by actual cameras, and
discover that there are a lot of variables that our brains have been adjusting for
us behind the scenes.
One of the ways in which cameras and eyes can differ is their field of view.
Field of view is responsible for a lot of confusion in photography, and it has
some particularly significant effects on selfies.
When you hold a camera close to your face, it makes your features look
different. To understand why—and how it affects photos of all kinds—let’s talk
about supermoons.
Every now and then, viral internet stories make the rounds spreading wild
claims about some upcoming astronomical event.
These are sometimes accompanied by photos of the “supermoon” behind a
skyline, like this.
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So what happened? Was the first photo fake?
It might have been, but often it’s not. Instead, it’s a photo taken with a very
narrow angle, through a telephoto lens.
Every photo shows a certain field of view. A wide field of view shows stuff
off to the sides, and a narrow one shows only the objects directly in front of the
lens.
“Zooming in” means narrowing the field of view. It’s easy to think of
zooming in as “getting closer” to the subject, because it makes a small subject
get bigger and fill the frame. But zooming in isn’t quite the same as getting
closer. When you get closer to a subject, the subject gets bigger within the
picture, but the distant background stays the same size. When you zoom in, the
subject and the background get bigger.
The reason people get tricked by this difference is that our eyes have only one
field of view. We can focus our attention on something at the center of our
vision, but the total area covered by our eyes stays the same. Photos with
unusually wide or narrow fields of view can surprise us.
For decades, the rule of thumb among photographers has been that a 50mm
full-frame lens produces an image that looks “natural” to people—not too wide
and not too narrow. This “natural” lens produces a surprisingly narrow field of
view; it’s about 40° wide, similar to the area covered by a hardback book when
you hold it about a foot from your face.
But smartphones may be in the process of changing all that, because phone
cameras have much wider fields of view than old 50mm lenses.
The iPhone X, for example, has a 65° horizontal field of view, letting users fit
a wider scene into the frame without having to back up. (It is not, however, quite
wide enough for one common photography subject: rainbows. A rainbow covers
83° of the sky, making it slightly too wide to fit in an iPhone frame.)
These wider-angle lenses may have become more common because
smartphone users want to take natural-looking pictures of scenes from life, or
selfies that show multiple people. It’s hard to take a selfie with a traditional
50mm camera held at arm’s length. And phones make it easy to crop our images
after the fact, so it makes sense to err on the side of “too wide” and let users do
the zooming and cropping. But the wide field of view comes with a cost: when
you use a wide-angle lens to take a picture of a small or faraway subject, it may
not show you what you expect.
To a human, the Moon is attention-grabbing. Even if we don’t literally “zoom
in” with our eyes, we narrow our attention to isolate it. We use our highresolution vision to pick out the details of the Moon, ignoring the comparatively
boring sky around it.
But a smartphone doesn’t know to “narrow its focus” the way our brain does.
The Moon is just another patch of pixels, lost in its extra wide–angle camera. To
get a good photo of the Moon, you need to zoom in—something that
smartphones have limited ability to do.
If you do have a camera that can zoom in, all the other stuff you might want to
include in the picture—like buildings and trees around you—doesn’t fit in the
frame anymore. Those things look bigger than the Moon from where you’re
standing, even though they’re obviously not (unless your city has unusually lax
zoning regulations.)
If you want an object to appear small relative to the Moon, you have to move
far enough away that it takes up a smaller angle of the sky. For a building, this
distance can be pretty large. In order to take one of those photos that shows a
huge moon behind a city skyline, the photographer generally needs to stand
miles away from the city. That nice-looking photo probably took a huge amount
of work and planning.
The reason buildings look so big in ordinary photos, and the Moon looks so
small, is because buildings are so much closer than the Moon. And this brings us
back to selfies.
WIDE-ANGLE SELFIES
This same wide-angle effect that makes the Moon seem tiny can affect how
selfies turn out. When someone takes a photo of their face with a smartphone,
their instinct for composition might tell them to hold the phone close enough that
their face fills a significant portion of the frame. But at that distance, which is
much closer than where someone would usually stand when looking at you, the
wide-angle smartphone lens creates an unnatural perspective. Your nose and
cheeks are substantially closer to the camera than your ears and the rest of your
head, which makes them look bigger—just like a building in the foreground of a
smartphone shot looks bigger than the Moon.
This distortion can make faces look subtly different in ways that we don’t
expect. To reduce the effect, hold the phone farther away and zoom in—either
within the camera app as you take the picture, or after the fact by cropping it.
How far away should you hold the phone? To minimize perspective distortion
between several objects in a frame, the distance to the phone should be much
larger than the difference in distance between the nearest and farthest objects.
The difference between the distance to the nearest and farthest visible parts of
your face is probably less than a foot, which means that the distortion can
change a lot depending on whether you hold the camera up at a normal distance
from your face or stretch your arm out all the way. Holding a camera 5 or 6 feet
away will almost entirely eliminate this kind of distortion, but our arms aren’t
long enough for that—which partly helps to explain the popularity of selfie
sticks.
TAKE COOLER SELFIES BY MESSING WITH YOUR
FIELD OF VIEW
Perspective distortion can change the relative size of parts of your face, but
there’s another way it can affect your photos—one that can open up a whole new
variety of selfie options.
When you zoom in, you change the apparent size of objects in the
background. If you’re standing in front of a large object that’s far away, such as
a mountain, the camera’s zoom can dramatically affect how big the mountain
looks.
If you set up your camera on a timer and walk far away from it, you can make
even a fairly small mountain look huge.
MOON SELFIE
Smartphone cameras have limits to how far they can zoom, but if you get a
camera with a powerful telephoto zoom lens, you can take some really
interesting selfies. You can even recreate those Moon skyline photos—but using
your own body instead of a building.
We can use geometry to work out how far away your camera needs to be in
order to take a photo of yourself in front of the Moon.
This tells us that the camera needs to be about 600 feet away to take a Moon
selfie.
Since they don’t make selfie sticks that are 600 feet long, you’ll probably
want to set up the camera on some kind of tripod and trigger it remotely.
Lining up a photo like this can be tricky; you need to find an area with a high
place to stand and a long, unobstructed view path in the opposite direction from
the Moon. The Moon moves quickly, so once everything is lined up, you’ll only
have a short window to take a photo—about 30 seconds. It only takes a little
over two minutes for the Moon to move out of view completely.*
With the right filters, if you’re extremely careful, you can even take a photo
like this of the Sun. This may destroy your camera, so consult with your local
astronomy club or photography store before trying this yourself. If you don’t,
there’s a good chance you’ll set your camera on fire. And never look through an
optical viewfinder when you’re pointing a camera at the Sun. Your eye may not
work exactly like a camera, but it’s just as easy to burn a hole in.
VENUS/JUPITER SELFIE
In principle, you can take a similar photo using even smaller, more distant
objects. After the Sun and Moon, the celestial bodies that appear largest in the
sky are Jupiter and Venus, which are both around an arcminute in size when
close to the Earth and most visible. Using the same geometry from the Moon
example, you can work out how far away you’ll need to hold the camera in order
to take a selfie with Venus or Jupiter: about 4 miles.
Holding a camera 4 miles away will present some obvious challenges.
Atmospheric distortion is greatest when Venus is closest to the horizon, so
you’ll want it to be relatively high in the sky—which means you’ll need to be
high above the camera. But you want the camera to be fairly high up as well, to
get it out of the thick atmosphere.
A good setup would consist of a camera on a mountaintop, with the subject
standing on a much higher mountaintop. But finding two climbable mountains
the right distance apart that align with Venus on a particular day will take a lot of
survey work and planning. You could try to avoid the alignment problem by
positioning yourself on a high-altitude aircraft or balloon, but maneuvering to
get yourself in the right position will be extremely difficult and will probably
require computer control.
Regardless of which method you choose, getting the alignment right will be
an extremely difficult challenge, and whatever picture you take is going to be
pretty blurry. Even under the best of conditions, it’s difficult to take a sharp
picture of Jupiter or Venus from the ground due to atmospheric distortion. It’s
possible no one has managed to take a selfie like this, so if you do, you’ll
definitely earn internet bragging rights.
A selfie with Jupiter or Venus would push the bounds of optics and geometry,
and would be pretty hard to top . . . from Earth, that is. If you travel to space,
where atmospheric distortion is less of a problem, you can open up new selfie
possibilities.
There are several telephoto cameras in space with very high angular
resolution, although you may have trouble convincing NASA to let you borrow
them.*
But there’s a way to take a space selfie with an even longer “zoom” than the
fanciest space telescope. It’s called occultation, and it’s one of the coolest tricks
in astronomy.
OCCULTATION SELFIES
When an asteroid passes in front of a star from the point of view of Earth, people
with stopwatches scattered around the world can time when the star disappears
and reappears, and use those measurements to build up a picture of the asteroid.
This technique can be used to see detail too small or faint for the fanciest
telescopes to make out. And it could, in theory, let you take an incredibly distant
selfie while in space. All you need is a network of friends on the ground to
watch a distant star blink out as you drift in front of it.
Using a distant star, your friends could take a photo of you from a distance of
up to several hundred miles. You won’t be able to go any farther than that
because your shadow will be lost to diffraction. If you use a distant X-ray source
instead of a visible star, the shorter wavelength will reduce the effects of
diffraction, and you could conceivably take a picture of yourself standing on the
surface of the Moon while your friends observed from the ground.
Just remember: orbital alignments used for occultations are rare and usually
don’t repeat, so they take a huge amount of planning—which means you’ll only
get one shot.

CHAPTER 22
How to Catch a Drone
(with sports equipment)
A wedding-photography drone is buzzing around above you. You don’t know
what it’s doing there and you want it to stop.
Let’s assume you don’t have any kind of sophisticated anti-drone equipment,
like net launchers, shotguns, radio jammers, mist nets, counter-drone drones, or
other such specialized gear.
If you do have a very well-trained bird of prey, you may think it’s a good idea
to send it after the drone. Every now and then, videos circulate around the
internet showing trained birds of prey snatching drones out of the sky. This is a
concept we find instinctively satisfying, but any plan that calls for countering
rogue machines by training animals to hurl themselves at them is probably a bad
one. We wouldn’t enforce speed limits by training cheetahs to leap onto
motorcycles. It would be cruel and dangerous to the cheetahs, and besides, there
are a lot more motorcycles than there are cheetahs. Earth’s MOTORCYCLE :
CHEETAH ratio (MpC) has never been precisely calculated, but it’s probably
several hundred thousand.
Similarly, there are certainly more drones in the world than birds of prey—
and new drones are being produced a lot faster than new birds of prey. Earth’s
DRONE : HAWK ratio is harder to estimate than its MpC, but it’s almost certainly
greater than 1.
If falcons are a bad idea, what else might you use?
Drones are up in the air, so you want to send an object flying through the air.
Humans send objects flying through the air all the time in the world of sports—
see chapter 10: How to Throw Things for instructions.
Let’s suppose you have a garage full of sports equipment—baseballs, tennis
rackets, lawn darts,* you name it. Which sport’s projectiles would work best for
hitting a drone? And who would make the best anti-drone guard? A baseball
pitcher? A basketball player? A tennis player? A golfer? Someone else?
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A lot of drones are pretty fragile, so let’s assume for the moment that as long
as you can hit it, you’ll cause it to crash. (This has certainly been my
experience.)
For the purpose of approximate comparisons, we’ll use a simple number to
rate the accuracy of projectiles across different sports, representing the ratio of
range to error. If you throw a ball at a target 10 feet away, and you miss by an
average of 2 feet, then you have an accuracy ratio of 10 divided by 2, or 5.
The body of a medium-size drone—like the DJI Mavik Pro—has a “target
area” about a foot across, meaning we can miss the center of the drone by 6
inches in either direction. If it’s hovering 40 feet away, we’ll need an accuracy
ratio of 80 to be likely to hit it—or somewhat less if the projectile is larger, since
that gives us more room for error.
Shots in which the projectile travels in a high arc, like in basketball or golf,
gain additional accuracy, since the drone’s wide and flat shape presents more of
a target. And large projectiles, like footballs and basketballs, have more margin
of error.
Here are some estimated accuracy ratios for various athletes, based on
competition play, exhibitions, or scientific studies in which athletes tried to hit
targets.
Athlete Estimated
accuracy ratio
Attempts required to hit DJI
Mavic Pro at 40 feet
Based on
Soccer kicker 21 13 Study of 20 experienced
Australian players
Placekicker 23 15 NFL kickers in the late 2010s
Recreational hockey
player
24 35 25 recreational and university
hockey players
Basketball
(Shaquille O’Neal)
36 4 NBA free throw percentage
Golf drive/chip 40 6* PGA drive accuracy stats
Basketball (Steph
Curry)
63 2 NBA free throw percentage
NHL All-Star 50 9 NHL accuracy shooting
NFL QB passing 70 4 Pro Bowl precision passing
typical score*
High school pitcher 72 3 Study of 8 Japanese high
Professional pitcher 100 2 school pitchers
Darts champion 200-450 1* PDC analysis of Michael van
Gerwen
Olympic archer 2,800 1 2016 Korean men’s archery
team
Clearly, archers are the best choice, if you can find one. Their combination of
extreme precision and long range would make them ideal defenders. Pitchers
would also be a great choice—and a baseball would probably do a lot of
damage. Basketball players make up for their lower accuracy with a large
projectile and efficient arcing shot. Hockey players, golfers, and kickers are all
probably less than ideal choices.
I was curious to test this in the real world, and one sport I couldn’t find good
data on was tennis. I found some studies of tennis pro accuracy, but they
involved hitting targets marked on the court, rather than in the air.
So I reached out to Serena Williams.
To my pleasant surprise, she was happy to help out. Her husband, Alexis,
offered a sacrificial drone, a DJI Mavic Pro 2 with a broken camera. They
headed out to her practice court to see how effective the world’s best tennis
player would be at fending off a robot invasion.
The few studies I could find suggested tennis players would score relatively
low compared to athletes who threw projectiles—more like kickers than
pitchers. My tentative guess was that a champion player would have an accuracy
ratio around 50 when serving, and take 5–7 tries to hit a drone from 40 feet.
(Would a tennis ball even knock down a drone? Maybe it would just ricochet off
and cause the drone to wobble! I had so many questions.)
Alexis flew the drone over the net and hovered there, while Serena served
from the baseline.
Her first serve went low. The second zipped past the drone to one side.
The third serve scored a direct hit on one of the propellers. The drone spun,
momentarily seemed like it might stay in the air, then flipped over and smashed
into the court. Serena started laughing as Alexis walked over to investigate the
crash site, where the drone lay on the court near several propeller fragments.
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Even though it’s just a machine, a drone lying on the ground seems oddly
tragic.
“I felt really bad hurting him,” Serena said, after the pieces had been
collected. “Poor little guy.”
I couldn’t help but wonder: Is it wrong to hit a drone with a tennis ball?
I decided to ask an expert. I contacted Dr. Kate Darling, robot ethicist at the
MIT Media Lab, and asked her if it’s wrong to hit tennis balls at a drone for fun.
She said, “The drone won’t care, but other people might.” She pointed out that
while our robots obviously don’t have feelings, we humans do. “We tend to treat
robots like they’re alive, even though we know they’re just machines. So you
might want to think twice about violence towards robots as their design gets
more lifelike; it could start to make people uncomfortable.”
That made sense, but on the other hand, should we really be making ourselves
so vulnerable?
“If you’re trying to punish the robot,” she said, “you’re barking up the wrong
tree.”
She has a point. It’s not the robots we need to worry about, it’s the people
controlling them.
If you want to bring down a drone, perhaps you should consider a different
target.
CHAPTER 23
How to Tell If You’re a Nineties Kid
When were you born?
For most people, this is an easy question. Even those who don’t know their
exact birthday can usually tell when they were born to within a few years.
Yet the internet is full of quizzes that promise to help you determine which
decade you were born in. These are usually based on what was happening in
American pop culture at the time you first became aware of it.
Of course, these quizzes aren’t really about helping you find out when you
were born. They’re about giving you a sense that there’s a group out there that
you belong to, reinforced by shared memories.
Movies and TV shows aimed at children are particularly well suited for this
kind of quiz, not only because childhood memories are a source of nostalgia, but
also because kids’ shows often target a very limited age range, producing narrow
“generational” distinctions. The mix of media you grew up with is often a unique
fingerprint that shows your age down to within a few years. People born in the
early to mid-1980s, for example, might remember the early “Disney
Renaissance” movies as particularly formative—The Little Mermaid (1989),
Beauty and the Beast (1991), and Aladdin (1992). On the other hand, those born
in the late 1980s might have more-vivid, formative memories of The Lion King
(1994) and Toy Story (1995). People born in the early 1980s were largely too old
for the late-1990s Pokémon craze, while those born in the late 1980s were too
young to listen to New Kids on the Block.
Clearly, there’s a demand for these kinds of roundabout ways to identify your
age. But why stop at movies and TV shows? The world is changing all the time
in ways that leave a mark on us.
CHICKEN POX PARTIES
Chicken pox is an itchy rash, caused by the varicella-zoster virus, which lasts for
a few weeks. After someone is infected once, they generally become immune to
new infections for life (although the latent infection can flare up later in life,
causing a painful rash called shingles).
For most of the 20th century, virtually everyone got chicken pox by the time
they reached adulthood. Since the disease is more severe in adults than children,
parents preferred to let their kids get exposed early—by throwing “chicken pox
parties”—to gain immunity and avoid a risky later-in-life infection. Then
everything changed* in 1995, when a chicken pox vaccine became available.
In the 10 years following its introduction, chicken pox vaccination rates
climbed to near 100 percent, and chicken pox cases plummeted.
Within 20 years of the introduction of the vaccine, chicken pox went from
universal to rare. For those born in the United States after the mid-1990s, it’s
seen as an old-timey disease, like polio. If you remember chicken pox and
chicken pox parties, you were probably born in the 1990s or earlier.
SCARS
Chicken pox occasionally leaves lasting scars, but the chicken pox vaccine
typically does not. Other vaccines left a physical mark on the generations that
received them.
Smallpox, a disease caused by another virus, may well be responsible for the
largest death toll of any human infectious disease. When Europeans arrived in
the Americas, they brought smallpox with them—along with other diseases like
hepatitis—into an area where the people had no natural immunity and were
especially susceptible. The diseases swept across the continent, killing most of
the people who lived there. The true death toll from smallpox is unknown, but it
killed hundreds of millions of people in the 20th century alone.
Without its human hosts, the virus cannot survive. The first vaccine for
smallpox was developed at the end of the 18th century, and by the end of the
19th century, the disease had become comparatively rare in most industrialized
countries. In the 20th century, medical advances made the vaccine easier to
produce and transport around the world, leading to a global campaign to
eradicate smallpox completely. It succeeded: the last smallpox infection “in the
wild” occurred in Somalia in 1977, and the last outbreak in history—and the
final smallpox death—happened after a lab accident in 1978.
The smallpox vaccine is administered with a double-pointed needle, which
breaks the skin in several places and deposits the vaccine:
The vaccine contains a milder virus that causes the body to react as it would to
a real smallpox infection, resulting in swelling, a blister, and a scab. After a few
weeks, the wound heals, leaving a distinctive round scar.
The last case of smallpox in the United States was in 1949, and routine
childhood smallpox vaccination in the United States and Canada ended in 1972.
If you’re from the United States or Canada and have that vaccination mark on
your upper arm or outer leg, it means you were born before about 1970.* The
circular mark is a battle scar from humanity’s war against one of our most
terrible foes. And if you don’t carry such a scar, that’s a testament to our victory.
YOUR NAME
Baby names generally rise and fall in popularity over time.
Some names are relatively timeless; Elizabeth, Marshall, Susanna, Nina, and
Nelson have been consistent in popularity in the United States over many
generations. Biblical names, like John, James, and Joseph, are also relatively
timeless. But changes in naming patterns can really sneak up on you. The
biblical name Sarah was one of the most popular names in the United States in
the 1980s, but by the mid-2010s there were more babies in the United States
being named “Brooklyn” than “Sarah.”
Here’s a list of some of the most common generationally specific names for
every five years. These are names that had a relatively narrow peak in
popularity, within just a decade or so. If you were born in the United States
around this year, these are names that are more likely to seem common and
generic to you, but are distinctive generational markers.
1880 Will, Maude, Minnie, May, Cora, Ida, Lula, Hattie, Jennie, Ada
1885 Grover, Maude, Will, Minnie, Lizzie, Effie, May, Cora, Lula, Nettie
1890 Maude, May, Minnie, Effie, Mabel, Bessie, Nettie, Hattie, Lula, Cora
1895 Maude, Mabel, Minnie, Bessie, Mamie, Myrtle, Hattie, Pearl, Ethel, Bertha
1900 Mabel, Myrtle, Bessie, Mamie, Pearl, Blanche, Gertrude, Ethel, Minnie, Gladys
1905 Gladys, Viola, Mabel, Myrtle, Gertrude, Pearl, Bessie, Blanche, Mamie, Ethel
1910 Thelma, Gladys, Viola, Mildred, Beatrice, Lucille, Gertrude, Agnes, Hazel, Ethel
1915 Mildred, Lucille, Thelma, Helen, Bernice, Pauline, Eleanor, Beatrice, Ruth, Dorothy
1920 Marjorie, Dorothy, Mildred, Lucille, Warren, Thelma, Bernice, Virginia, Helen, June
1925 Doris, June, Betty, Marjorie, Dorothy, Lorraine, Lois, Norma, Virginia, Juanita
1930 Dolores, Betty, Joan, Billie, Doris, Norma, Lois, Billy, June, Marilyn
1935 Shirley, Marlene, Joan, Dolores, Marilyn, Bobby, Betty, Billy, Joyce, Beverly
1940 Carole, Judith, Judy, Carol, Joyce, Barbara, Joan, Carolyn, Shirley, Jerry
1945 Judy, Judith, Linda, Carol, Sharon, Sandra, Carolyn, Larry, Janice, Dennis
1950 Linda, Deborah, Gail, Judy, Gary, Larry, Diane, Dennis, Brenda, Janice
1955 Debra, Deborah, Cathy, Kathy, Pamela, Randy, Kim, Cynthia, Diane, Cheryl
1960 Debbie, Kim, Terri, Cindy, Kathy, Cathy, Laurie, Lori, Debra, Ricky
1965 Lisa, Tammy, Lori, Todd, Kim, Rhonda, Tracy, Tina, Dawn, Michele
1970 Tammy, Tonya, Tracy, Todd, Dawn, Tina, Stacey, Stacy, Michele, Lisa
1975 Chad, Jason, Tonya, Heather, Jennifer, Amy, Stacy, Shannon, Stacey, Tara
1980 Brandy, Crystal, April, Jason, Jeremy, Erin, Tiffany, Jamie, Melissa, Jennifer
1985 Krystal, Lindsay, Ashley, Lindsey, Dustin, Jessica, Amanda, Tiffany, Crystal, Amber
1990 Brittany, Chelsea, Kelsey, Cody, Ashley, Courtney, Kayla, Kyle, Megan, Jessica
1995 Taylor, Kelsey, Dakota, Austin, Haley, Cody, Tyler, Shelby, Brittany, Kayla
2000 Destiny, Madison, Haley, Sydney, Alexis, Kaitlyn, Hunter, Brianna, Hannah, Alyssa
2005 Aidan, Diego, Gavin, Hailey, Ethan, Madison, Ava, Isabella, Jayden, Aiden
2010 Jayden, Aiden, Nevaeh, Addison, Brayden, Landon, Peyton, Isabella, Ava, Liam
2015 Aria, Harper, Scarlett, Jaxon, Grayson, Lincoln, Hudson, Liam, Zoey, Layla
If kids in your class were named Jeff, Lisa, Michael, Karen, and David, then
you were probably born in the mid-1960s. If they were named Jayden, Isabella,
Sophia, Ava, and Ethan, then you were probably born somewhere around 2010.
But names can reveal things about age in other ways.
The mid-1990s TV show Friends featured six roommates, played by actors,
named Matthew, Jennifer, Courtney, Lisa, David, and another Matthew. Each of
those names has its own popularity curve; if we combine them all, we can guess
what years the group of actors was likely born:
The actors were actually born in the late 1960s, on the very early edge of the
popularity of their names. In other words, the actors all have names that were a
little before their time. Courtney Cox and Jennifer Aniston had names that didn’t
really become popular until a decade later. (Maybe people with trendy parents
are more likely to wind up in acting.) But the names are generally consistent
with their era, if a little ahead of the curve.
We get something very different if we look at the names of their characters—
Phoebe, Joseph, Ross, Chandler, Rachel, and Monica:
The show debuted in 1994. There’s a clear spike in popularity of the names in
1995 and 1996, which can probably be attributed to the show putting the names
in the minds of new parents. But it’s not just the show—that name combination
was clearly on the rise in the years before Friends premiered. It’s possible that
parents looking for good names for their children are influenced by some of the
same cultural trends as TV writers looking for good names for their characters.
RADIOACTIVE TEETH
Humans invented nuclear weapons in 1945. We detonated the first one to test
whether they worked, then used another two in war. Once that war was over, we
set off a few thousand more of them just to see what would happen.
We learned a lot about nuclear weapons from these tests. One thing we
learned was, “Setting off nuclear weapons fills the atmosphere with radioactive
dust.” We also learned that nuclear weapons could be made much more
powerful. In fact, there was effectively no limit on how powerful we could make
them, which was a little alarming. The United States and the Soviet Union
quickly developed arsenals large enough to, effectively, end the world. The
knowledge that distant humans could trigger a fiery apocalypse at any moment at
the push of a button left a strong impression on the children of the 1950s and
1960s.
But the impression it left was physical as well as psychological.
Most of the atmospheric nuclear explosions happened in the mid- to late
1950s, with a few more truly gigantic ones in 1961 and 1962. Amid increasing
concerns about radioactive contamination, the United States and USSR agreed to
stop all above ground testing and limit themselves to underground tests. They
signed the Limited Nuclear Test Ban Treaty in 1963, which ended the era of
large-scale atmospheric nuclear tests. Over the next few decades, there were
only a few more atmospheric nuclear tests by France and China. The final
nuclear explosion in the Earth’s atmosphere was a Chinese test on October 16,
1980.*
The radioactive debris released by these explosions spread throughout the
atmosphere. It consisted of a wide variety of radioactive elements. Some, like
cesium-137, accumulated in human bodies and caused cancer. Others, like
carbon-14, were harmless to human health, but caused annoyance to
archaeologists by messing with carbon dating.
Carbon-14 is naturally produced by cosmic rays interacting with the
atmosphere, and decays into nitrogen-14 with a half-life of about 5,700 years. At
any given time, a tiny fraction of the carbon in the atmosphere is carbon-14; the
rest is carbon-12 and carbon-13. Other than its limited lifespan, carbon-14 acts
just like its stable cousins, and is incorporated into organic* material without
causing problems. When an organism dies, its biological processes stop
exchanging carbon with the atmosphere, and the carbon-14 starts to decay. By
measuring how much carbon-14 is left in an archaeological specimen, we can
determine how long ago it stopped getting a fresh supply of carbon-14. In other
words, we can figure out when it died.
This trick—carbon dating—is only possible if we know the original
concentration of carbon-14 in the atmosphere when the organism was alive.
Since carbon-14 is produced by cosmic rays, its concentration seems to have
been relatively stable over time . . . until we came along. Nuclear testing injected
a huge amount of carbon-14 into the atmosphere:
Any future archaeologists trying to carbon-date organic specimens will need
to account for the massive 20th-century spike, or they’ll calculate the wrong date
for everything they dig up.
Another contaminant released by nuclear testing was strontium-90. Since
strontium is similar to calcium, our bodies incorporate it into teeth and bones.
People who were children in the 1960s absorbed a lot of strontium. Researchers
collected baby teeth throughout the 1950s and 1960s* and tested them for
strontium-90, confirming the contamination and helping to make the case for a
moratorium on atmospheric testing.
Atmospheric levels of strontium-90 declined after the early 1960s. Over time,
the high strontium levels in the skeletons of the baby boomers fell, as the
strontium was removed by the natural process of bone renewal. By the 1990s,
baby boomers and children had similar levels of strontium in their bones.
Teeth, on the other hand, are more compact and stable than bones, and don’t
undergo natural renewal at the same rate that bones do. People whose permanent
teeth were forming in the early 1960s likely carry ever-so-slightly elevated
strontium-90 levels to this day.
In the same way that nuclear testing filled the atmosphere with radioactive
fallout, the burning of leaded gasoline contaminated the air with lead. This led to
a mid-20th-century lead poisoning epidemic, which peaked around 1972. The
median childhood blood lead level in the late 1970s was 15 micrograms per
deciliter, and it was probably even higher earlier in the decade. Children in many
areas had lead levels above 20 µg/dL, levels that we now know to cause
significant harm to developing brains. Studies suggest that lead in tooth enamel
isn’t exchanged with the environment, so baby boomers and Gen-Xers likely
have elevated amounts of lead in their permanent teeth as well. These trace
amounts of strontium and lead are now too small to have any real health effects,
but we carry them with us as souvenirs.
Most of the contaminants from the mid-20th century are fading from the
environment. Elements like iodine-131 emit a lot of radiation in the first few
months but quickly decay. The longer-lived carbon-14 is being removed by the
natural carbon cycle, and carbon-14 is almost back to its “natural” levels.*
Strontium-90 has a half-life of around 30 years, as does cesium-137, another
major source of contamination. As of the publication of this book, a quarter of
the strontium-90 and cesium-137 from the 1960s nuclear tests remains.
But even as the radioactive elements settle out of the environment and slowly
decay into more-inert forms, their imprint is left on us. No one really knows how
many people have died from cancer caused by nuclear testing. The low estimates
are in the thousands. The high estimates are in the hundreds of thousands. The
quiet, hidden death toll from these weapons tests may well be greater than the
death toll from the bombings of Hiroshima and Nagasaki. The legacy of the
choices we made in that short period after World War II will be with us for a
long time.
So if you want to know whether you’re a 1990s kid or a 1950s kid, check your
teeth.
CHAPTER 24
How to Win an Election
To win an election, you have to convince lots of people to choose your name on
a ballot. There are two general approaches you could follow:
Convincing lots of voters to support you
Tricking them into picking your name on the ballot by mistake
The first approach typically requires some combination of charm, personal
charisma, competence, a compelling message, and the presentation of a clear
choice between competing visions for the future. Those are all a lot of work, so
let’s start by considering the second one.
TRICK VOTERS INTO PICKING YOUR NAME BY
MISTAKE
This electoral strategy has been popular over the years, despite the generally
mixed results.
In 2016, a Canadian man from Thornhill, Ontario, spent $137 to legally
change his name to “Above Znoneofthe,” and filed to run in a provincial
election. He intended to be listed on the ballot as “ZNONEOFTHE ABOVE,”
with the Z included to put him at the end of the alphabetical list of names,
hoping that people would mistake his name for a “None of the above” option.
Unfortunately for him, while the names on the ballot were alphabetized by last
name, they were printed in <first name> <last name> order. He appeared in the
ballot as “Above Znoneofthe.” Mr. Znoneofthe did not prevail.
If you’re running for a minor local office, it’s possible that a large portion of
voters won’t know who you are, especially if you run in a year when there’s a
big election that draws lots of turnout.* In these situations, many voters might
have nothing to judge you by except your name.
Occasionally, this has caused confusion—and created opportunities. In 2018,
Kansas congressman Ron Estes ran for reelection, only to be challenged in the
Republican primary by a political newcomer who was also named Ron Estes.
The second Ron Estes was listed on the ballot as Ron M. Estes. The
incumbent Ron changed his campaign signs to list him as “Rep. Ron Estes” and
ran ads informing voters that the M stood for “Misleading.” The other Ron
retaliated by telling voters it stood for “’Merica.”
In the end, the name gimmick didn’t work. When the primary finally arrived,
Ron Two was soundly defeated by Ron Prime.
But name games have occasionally been successful—just ask Bob Casey.
From 1960 into the 21st century, Pennsylvania has voted for five different
people named Bob Casey in statewide or federal elections, and it’s not entirely
clear that voters always chose the Bob Casey they intended.
Here’s a quick rundown of the Bob Caseys* of Pennsylvania:
Bob Casey #1: a lawyer from Scranton
Bob Casey #2: Cambria County Recorder of Deeds
Bob Casey #3: a PR consultant
Bob Casey #4: a schoolteacher and ice cream seller
Bob Casey #5: son of Bob Casey #1
Starting in the 1960s, Bob Casey #1 was elected to a number of state offices,
quickly becoming a rising star in state politics. In 1976, the state held an election
for treasurer. Bob Casey #1, then the state auditor, was eying a campaign for
governor in 1978, so he decided not to run for treasurer . . . but Bob Casey #2—a
Cambria County official—did.
The same year, Bob Casey #3 ran for Congress in Pennsylvania’s 18th district.
His opponent complained that he was just trying to take advantage of Bob Casey
#1’s popularity. Bob Casey #3 retorted that Bob Casey #2 was cashing in on the
collective popularity of himself and Bob Casey #1, the real Caseys. Bob Casey
#3 ended up winning the Republican nomination, but lost the general election to
the Democrat.
As for Bob Casey #2, despite barely campaigning, he also won his primary,
defeating Catherine Knoll—the party-endorsed candidate—and several others.
Knoll’s campaign spent $103,448; Casey spent $865.
Casey went on to win the general election and serve a four-year term as
treasurer. The Republicans began a campaign to inform the public that “Bob
Casey” wasn’t who they thought he was, and their nominee—Budd Dwyer—
defeated Casey #2 in 1980.*
In 1978, during Bob Casey #2’s term as treasurer, Bob Casey #1 launched a
bid for governor. Unfortunately, this was the same year Bob Casey #4—a
schoolteacher and ice cream seller from Pittsburgh—appeared on the scene. Bob
Casey #1 ran for governor, but Bob Casey #4 ran for lieutenant governor in the
same primary. Voters, possibly thinking that Bob Casey #1 was making himself
available for both positions,* nominated Bob Casey #4 lieutenant governor, but
chose Pete Flaherty over Bob Casey #1 for governor. In the end, the Flaherty–
Casey #4 ticket lost the general election.
In 1986, Bob Casey #1 ran for governor again, branding himself as “The Real
Bob Casey,” and finally won.* He served for eight years as governor before
leaving office in 1994. Two years later, Bob Casey #5—his son, Bob Casey Jr.
—ran for auditor and won. He went on to become state treasurer and eventually
senator, a position he was reelected to in 2018.
So if you’re going to run for office, try changing your name to Bob Casey.
You never know!
CONVINCING LOTS OF VOTERS TO SUPPORT YOU
Winning elections is hard. The truth is, people are complicated, there are a lot of
them, and no one is ever 100 percent sure why they do what they do or what
they’re going to do next.
But if your goal is simply to win an election, then as a general rule you should
be for things that voters like and against things they dislike. To do that, you’ll
need to figure out what the voters like and dislike.
One of the most popular tools for figuring out what the public thinks is
opinion polling—talking to a bunch of people, asking them what they think, and
tallying up the results.
The website FiveThirtyEight has conducted an exercise in which they had
professional speechwriters write a speech that simply pandered as much as
possible—only making statements that most voters support, to pander either to
one party or to the electorate in general.
But what do we agree on the most? If your goal is simply to be in favor of
popular things and against unpopular things, what should you campaign on?
What are the least controversial issues in the country?
To help figure this out, I reached out to Kathleen Weldon, director of data
operations and communications at the Roper Center for Public Opinion Research
at Cornell University, to commission a poll of their polls. The Roper Center
maintains a tremendous database of opinion polling data—over 700,000 polling
questions spanning almost a century of opinion polling, collected from virtually
every organization that has ever conducted a public poll in the United States.
I told them I was looking for the most one-sided questions in their polling
database—the questions where virtually everyone gave the same answer. In a
sense, these would be the least divisive issues in the country.
The Roper research staff sifted through their database of 700,000 questions
and assembled a list of those questions for which at least 95 percent of
respondents gave the same answer.
It’s pretty rare for that many respondents to agree on anything in a poll. A
small percentage of respondents will often choose ridiculous answers because
they’re not taking the poll seriously, or because they misunderstand the question.
But one-sided questions are also rare because no one bothers to conduct polls on
uncontroversial topics unless they’re trying to prove a point. Since everything in
the Roper database is something that some person or organization bothered to
commission a poll to ask, it means it’s at least potentially controversial, if not
actually so.
Here is a selection of the most one-sided issues in the history of polling. If you
want to run for office, these are views you can safely espouse, secure in the
knowledge that at least one scientific survey puts the people squarely behind
you:
Popular Opinions
According to actual data (Full question text in endnotes)
95% disapprove of people using cell phones in movie theaters. (Pew Research
Center’s American Trends Panel poll, 2014)
97% believe there should be laws against texting while driving. (The New York
Times / CBS News Poll, 2009)
96% have a positive impression of small business. (Gallup Poll, 2016)
95% believe employers should not be able to access the DNA of their
employees without permission. (Time / CNN / Yankelovich Partners Poll,
1998)
95% support laws against money laundering involving terrorism. (ABC News /
Washington Post Poll, 2001)
95% think doctors should be licensed. (Private Initiatives & Public Values,
1981)
95% would support going to war if the United States were invaded. (Harris
Survey, 1971)
96% oppose legalizing crystal meth. (CNN / ORC International Poll, 2014)
95% are satisfied with their friends. (Associated Press / Media General Poll,
1984)
95% say that “if a pill were available that made you twice as good looking as
you are now, but only half as smart,” they would not take it. (Men’s
Health Work Survey, 2000)
98% believe lifeguards should watch swimmers rather than reading or talking
on the phone. (American Red Cross Water Safety Poll, 2013)
99% think it’s wrong for employees to steal expensive equipment from their
workplace. (Wall Street Journal / NBC News Poll, 1995)
95% think it’s wrong to pay someone to do a term paper for you. (Wall Street
Journal / NBC News Poll, 1995)
98% would like to see a decline in hunger in the world. (Harris Survey, 1983)
97% would like to see a decline in terrorism and violence. (Harris Survey,
1983)
98% would like to see a decline in high unemployment. (Harris Survey, 1982)
97% would like to see an end to all wars. (Harris Survey, 1981)
95% would like to see a decline in prejudice. (Harris Survey, 1977)
95% don’t believe Magic Eight Balls can predict the future. (Shell Poll, 1998)
96% think the Olympics are a great sports competition. (Atlanta Journal
Constitution Poll, 1996)
You can use this list to assemble a campaign platform. For example, you
could stand firmly against hunger, war, and terrorism; for friendship and small
business; and against texting while driving. You could support laws that ensure
doctors are properly licensed, and oppose allowing other countries to invade.
On the other hand, if you wanted to lose an election as spectacularly as
possible, this list could be even more helpful as a blueprint. By taking the
opposing position on each issue, you could potentially run the most unpopular
political campaign in political history. You’d probably lose, but in a world that
has nominated at least five different Bob Caseys, who knows!

CHAPTER 25
How to Decorate a Tree
About three-quarters of American households decorate trees for Christmas.
As of 2014, two-thirds of those households use artificial trees, while one-third
use real live trees. The vast majority of people who use real trees get them from
Christmas tree farms, but the traditional method—according to mid-20th-century
Christmas films, anyway—is to simply walk out into the woods and find a
suitable tree to cut down.
Depending where you are, you may not find a forest nearby. Forests are
distributed a little irregularly around the world. Most of the world’s forests are
concentrated along the equator and in the polar latitudes. The forests of the
equator and the poles are separated by bands of desert located around 30° north
and south of the equator.* If you’re near 30°N or 30°S, and you don’t see any
forests, try walking a few thousand miles toward the pole or the equator.
Once you locate a forest—and, ideally, obtain permission from the landowner
—your next challenge is selecting a Christmas tree.
But be careful what tree you cut down.
In 1964, University of North Carolina graduate student Donald Currey was
studying the history of glaciers in Nevada. A decade earlier, another scientist,
Edmund Schulman, had discovered some very old trees nearby. Some of the
bristlecone pines Schulman studied turned out to be between 3,000 and 5,000
years old—older than any other known trees.
Schulman’s ancient trees were in California’s White Mountains. Currey, over
the border in Nevada, found bristlecone pines as well, and suspected they were
of a similar age. He started sampling the trees, reasoning that their age could
reveal something about the history of the ice age he was studying. If the area had
cooled and the glaciers had expanded, the trees would have retreated down the
mountain—so the pines at the uphill edge of the grove should be relatively
young. He set about taking samples from some of the pines to determine their
age.
Accounts differ about exactly what happened next. Literature professor and
mountaineer Michael P. Cohen, in a 1998 book about the Great Basin, cataloged
five different versions of the incident from people involved, each one spinning
things a little differently.
All accounts agree on the central facts: Currey located a tree that seemed
especially old (unbeknownst to him, local naturalists had dubbed it
“Prometheus”) and obtained permission from the Forest Service to cut it down to
determine its precise age. After counting the rings from the trunk sections,
Currey determined that the bristlecone pine was at least 4,844 years old, making
it the world’s oldest known tree.
When Currey’s findings were published, public outcry ensued, and everyone
involved in the project spent the next several decades trying to explain why they
had killed the oldest tree on Earth.
The lesson of history is clear: before cutting down a tree, you may want to
make sure it’s not the oldest one in the world or people will get really mad.
Since the fall of Prometheus, the oldest dated tree has been another bristlecone
pine, dubbed “Methuselah.” Methuselah is at least 4,851 years old as of 2019,
which means it has recently exceeded Prometheus’s record.
These ages are determined from examining core samples, and so they only
give a lower limit on the true age, since some of the youngest parts of the tree
may not be represented in the core. University of Arizona researchers obtained
pieces of Prometheus’s trunk and determined that the tree was almost exactly
5,000 years old when it was cut down. That means it was . . . born? . . .
hatched? . . . sprouted? . . . germinated? . . . around 3037 BCE, followed by
Methusaleh some decades later. At the time the bristlecones first sprouted,
humans on the other side of the world were developing the first known writing
systems in Sumer.*
The forestry community is clearly hoping to avoid another Prometheus
incident. Methuselah isn’t exactly under round-the-clock armed guard, but its
exact identity and location remains a secret, to protect it from damage from
either souvenir hunters or—perhaps—copycat killers.
These bristlecone pines are certainly unique, but the truth is, they would make
terrible Christmas trees. You might think the trees that reach the greatest age are
the ones that grow in the healthiest and most supportive environments.
Surprisingly, the opposite is true. The oldest trees tend to be the ones that grow
in the worst conditions, not the best ones. When a bristlecone pine is in a
particularly harsh environment, one which blasts the trees with heat, cold, wind,
and salt, it slows their growth and development, stretching out their lifespans.
They weren’t very impressive to look at—the very oldest among them looked
like dead trees, with just a thin strip of bark running up one side, supporting a
few branches that clung to life. These ancient trees aren’t immortal—they’ve just
figured out how to die slowly.
If the world’s oldest tree would make a bad Christmas tree, what about the
world’s tallest?
US towns occasionally claim to host the world’s tallest Christmas tree.
According to Guinness World Records, that title belongs to a 67-meter Douglas
fir, erected in 1950 at a shopping mall in Seattle. Of course, like all such
seemingly trivial records, if you dig a little deeper you find a bitter controversy.
In 2013, the Los Angeles Times published a story on large Christmas trees, in
which tree farm owner John Egan accused the Seattle record of being bogus.
Egan claims that the Seattle record holder was not a real tree; rather, it was
constructed from several trees attached end-to-end. Egan claims that the real
record holder is a 41-meter tree his own company erected in 2007.
Regardless of who the real record holder is, Egan points out that the record
would be fairly easy to break. Someone just needs to go cut down a larger tree—
and there are plenty that are bigger than either contender.
The world’s tallest known tree is a coast redwood dubbed “Hyperion.”
Discovered in 2006, it stands just shy of 116 meters tall.* Bristlecone pines
aren’t the only record-setting tree in a witness protection program: Hyperion’s
exact location is kept quiet to protect it from harm, inasmuch as it’s possible to
hide something that tall.
But there are a number of trees of similar height. Before Hyperion’s
measurement was revealed in 2006, the record holder was the 113-meter
“Stratosphere Giant,” another northern California coast redwood.
There are several other trees near Hyperion around that height, over 110
meters, and any one of them would work about as well as a Christmas tree. After
all, who’s going to get mad at you for cutting down the world’s second-biggest
tree?
DISPLAYING THE TREE
Where should you put up your tree? It’s probably not going to fit in your house.
In fact, there are very few buildings where it will fit.
The US Capitol rotunda (55 meters) and the highest stadium domes (around
80 meters) are too short to fit a coast redwood Christmas tree. Even the long
halls of the biggest cathedrals, with nave heights of 40 or 50 meters, aren’t tall
enough. A Hyperion-size tree could just barely fit under the dome at St. Peter’s
Basilica at the Vatican, but only if you let the top poke into the lantern at the top
of the dome.
In Halbe, Germany, southeast of Berlin, there’s a former airship hangar that
has been converted into a tropical theme park. It features hundreds of feet of
sandy beaches, a rain forest section, and a water park. Unfortunately, the ceiling
of the park is just a few meters too short to fit the tallest redwoods. You could
still set up a tree there, but you’d need to dig out the floor first.
There are a few buildings with rooms large enough to hold a coast redwood
Christmas tree. The Basilica of Our Lady of Peace, in Yamoussoukro, Côte
d’Ivoire, is likely one of them. So are the atriums of several skyscrapers,
including Dubai’s Burj Al Arab (180 meters) and Beijing’s Leeza SOHO (190
meters).
Even if the owners wanted to display your Christmas tree, getting the tree
inside would be difficult, since the atriums of these buildings lack the necessary
giant doors.
Perhaps the ideal building for displaying a giant Christmas tree is one found in
the southeastern United States, on the east coast of Florida.
NASA constructed the Vehicle Assembly Building at Cape Canaveral as a
place to prepare the Apollo rockets and Space Shuttles for launch. It’s one of the
largest buildings in the world by volume, with a ceiling easily high enough to fit
your Christmas tree. And, crucially, there’s a way to get the tree inside—the
building has the tallest doors in the world.
The easiest way to get it there will probably be by ship. Luckily, the Panama
Canal is large enough to fit a boat carrying an intact 110-meter redwood lying on
its side.
The VAB is a perfect fit for our tree for a simple reason: it was designed to
hold the huge Saturn V rocket that took the Apollo astronauts to the Moon, and
that rocket was almost exactly the same size as the world’s tallest tree.

When fully loaded with fuel, the Saturn V rocket was substantially heavier
than a Hyperion-size tree. Since the rocket’s engines are capable of lifting it, that
means that if you attached them to the tree, they could lift it, too.
A pair of Space Shuttle booster rockets on either side would produce more
than enough thrust to lift your tree.

The tree itself would need some extra support. First, the tree will suffer from
the extreme vertical acceleration. Redwoods, the tallest trees in the world, have
to work to hold themselves up against gravity under the best of circumstances. A
rocket launch might subject the tree to several additional g’s of acceleration,
doubling or tripling the apparent force of gravity and causing the tree to buckle.
You can make things easier for the tree by pulling it instead of pushing it.
Wood, like many materials, is stronger in tension than compression. If you
attach the booster rockets partway up the trunk, the wood on the bottom half will
be under tension, since it’s dangling behind the rocket, while only the top half
will be under compression. By adding supports along the tree, you can help keep
it steady and prevent it from collapsing.

The rockets wouldn’t be able to get the tree going fast enough to stay in orbit,
but you could launch it on a suborbital trajectory that carried it over all those
other towns that claim to have the largest Christmas tree.
And your tree would be decorated with actual stars.

CHAPTER 26
How to Get Somewhere Fast
Getting around the world can be incredibly complicated.
Depending on where you are and where you’re going, you might be able to
travel to your destination quickly in a relatively straight line, or you might need
to go slowly and take an extremely roundabout route. Traveling can require
solving a staggering variety of problems, from the basics of walking through
doors to complicated tasks like navigating airport security, steering a car through
rush-hour traffic, or plotting rocket engine maneuvers for orbital transfers.
But one way or another, traveling to a destination eventually involves
accelerating yourself toward it. This acceleration puts a fundamental limit on
how fast you can get where you’re going.
Suppose you’re trying to travel between Point A—say, your front yard—and
Point B—say, a doctor’s appointment—under totally ideal circumstances. There
are no obstacles, no doors, no stop signs, and you have a magic scooter with
unlimited fuel. How fast can you travel from Point A to Point B?
Everything on Earth is being accelerated downward by the pull of gravity at
9.8 m/s
2
, or 1 G. When you accelerate forward in a vehicle, gravity is still
pulling you downward, so the total acceleration you feel is the combination of
the two—the horizontal push from the vehicle and the downward pull of gravity.
For small accelerations, the total acceleration you feel is about 1 G. If you
accelerate at 0.1 G, the total acceleration you feel is just 1.005 G, but if you
accelerate horizontally at 1 G, you feel a total acceleration of 1.41 G—as if
every part of your body suddenly weighed 41 percent more.
Human transportation methods, from legs to elevators to cars to airplanes,
usually involve horizontal accelerations of less than 1 G, for a few reasons. One
big reason is that humans evolved to experience 1 G of acceleration, and we find
it uncomfortable to spend much time accelerating faster than that. Another
reason is that vehicles often accelerate by pushing against the ground, and when
the horizontal push is stronger than the downward pull of gravity, the vehicle can
find itself spinning its wheels.*
Let’s assume your magic scooter is limited to accelerating at no more than 1
G. Real vehicles can and do accelerate faster than this on occasion, but generally
they’re specialty vehicles like rockets or roller coasters, and they only maintain
that acceleration for a short period of time. If we’re thinking about systems that
the general public might use to get around, a 1 G scooter serves as a good model
for the limits of what’s possible while maintaining some semblance of human
comfort and safety. Fighter pilots may be able to survive the sudden acceleration
of an ejection seat with only minor injuries, but you wouldn’t want to make one
part of your commute.
You hop on your scooter and check the clock. Your doctor’s office is 500
meters away, and your appointment starts in 10 seconds. Can you make it? You
turn up the throttle and accelerate toward the office.
The good news is that you’ll reach your appointment with many milliseconds
to spare. The bad news is that you’ll be traveling at over 200 mph when you
arrive.
Unless your doctor doesn’t mind very brief visits, you’ll need to slow back
down as you approach the office, which cuts into your total trip time. There are
limits to how quickly you can decelerate; stopping is generally easier than
starting—on virtually all land vehicles, from scooters to cars to taxiing airplanes,
brakes are more powerful than propulsion—but stopping too suddenly causes
just as many problems for your passengers as accelerating too fast.
If you spend the first half of your trip accelerating at 1 G and the second half
decelerating at 1 G, it will take you almost 15 seconds to reach your
appointment; if you leave 10 seconds before it starts, you won’t get there in time.
The limits faced by our magic scooter apply to any transportation method,
from moving walkways to bullet trains to futuristic vacuum tube people movers,
because they’re a function of human biology. No transportation system will ever
be able to carry people from a stationary position to a destination 500 meters
away in less than 10 seconds without accelerating them horizontally harder than
1 G.
What if your appointment is farther away? How quickly can your scooter get
you there?
At 1 G of continuous acceleration, speed adds up quickly. If you took a
minute-long trip at 1 G of acceleration—speeding up for 30 seconds, slowing
down for 30 seconds—you could travel more than 5 miles. Your peak speed,
halfway through your trip, would be close to the speed of sound.
Real trains don’t travel at near-supersonic speeds, but that’s not due to some
built-in limitation of physics. A platform on a rail can easily be accelerated up to
extremely high speeds through electromagnetic propulsion or rockets. Rocket
sleds running on rails at Holloman Air Force Base in New Mexico, for example,
have traveled as fast as Mach 8, eight times the speed of sound—faster than any
jet aircraft. To reach those speeds, the sleds accelerate much faster than 1 G—
and even so, they require a test track nearly 10 miles long.
At speeds near the speed of sound, air resistance becomes an unavoidable
problem—it’s hard for a vehicle to be efficient when it’s wasting so much
energy pushing its way through the air. That’s why the fastest vehicles tend to
operate high in the atmosphere, where the air is thin, or in vacuum tubes. Your
magic scooter, with its unlimited acceleration, doesn’t face any of these
problems, but hopefully it also has a good protective windshield. (You may also
want to apologize to any bystanders for the sonic booms.)
In 5 minutes, a 1 G scooter could carry you 137 miles, reaching speeds of over
Mach 4. In 10 minutes, you could travel 500 miles, reaching Mach 8. And in 48
minutes, you could travel halfway around the world.* This is the fundamental
limit for world travel—if you want to build a system that shuttles people to
anywhere in the world in under 48 minutes, it will have to involve accelerations
of more than 1 G (or drilling a hole through the Earth).
SPACE TRAVEL AT 1 G
These fundamental acceleration limits apply to spacecraft just as they do to Earth
vehicles. If you outfit your magic scooter to leave the atmosphere and travel
through space, accelerating and decelerating at 1 G, it will take you nearly 4
hours to make the trip to the Moon.
A 4-hour travel limit to the Moon tells us something interesting about the
future. Even in a world with space elevators and cheap space travel, large
numbers of humans living on Earth will probably not commute every day to the
Moon—or vice versa—for simple reasons of acceleration. Four hours each way
is a pretty long commute.
MORE DISTANT DESTINATIONS
It would take your 1 G scooter several days to reach any of the inner planets, a
week to reach Jupiter, and 9 days to reach Saturn.
The outer planets Uranus and Neptune are about two weeks away, and
reaching the more distant Kuiper Belt objects could take months.
Then things get weird.
AROUND THE UNIVERSE IN 80 YEARS
We don’t have any spacecraft technology right now that can accelerate a vehicle
at 1 G for long periods of time. There’s nothing in physics that says it’s
impossible, but no one has figured out a way to do it; none of the energy sources
we know of are small enough to be carried on a rocket yet powerful enough to
accelerate it for that long. But if we ever do find a way to do it, it will open up
the whole universe—thanks to a surprising boost from relativity. It turns out that
if you accelerate at 1 G for several years, you can reach almost any destination in
the universe.
If you accelerate at 1 G, your speed increases by 9.81 m/s every second. After
1 year, simple multiplication suggests you should be traveling at about 309
million m/s . . . which is 103 percent of the speed of light. Relativity tells us you
can’t really travel faster than light, so we know that’s wrong—you can get closer
and closer to the speed of light, but you can never quite reach it. Yet there aren’t
any cosmic police who show up and force you to stop accelerating, so what
actually happens to you?
Strangely, from your point of view, nothing happens as your scooter
approaches the speed of light. You just continue accelerating. But if you look out
at the universe around you, you’ll notice things getting a little strange.
As you go faster, the passage of time on board your scooter slows down. From
the perspective of an outside observer, your scooter flies past carrying slowly
ticking clocks and a slowly thinking brain. From your point of view, it seems to
take you less time than it should to reach successive landmarks along your trip—
as if the universe has contracted in the direction you’re traveling.
After a year has passed for you on your scooter, you’ll be traveling at about ¾
of the speed of light. But thanks to relativity, a year and two months will have
passed in the outside world, and your ship will have flown farther than you’d
expect.
The disparity between time on your scooter and time in the outside world
keeps growing. After 1½ years have passed on board, you’ll have traveled
almost 1½ light-years, the same distance light would travel in that time. After 2
years have passed for you, you’ll have gone more than 2 light-years, as if you’ve
traveled faster than light!
After a few years have passed on board, the effects of relativity really start to
add up. When 3 years have passed for you, a little over 10 years will have passed
outside the ship, and you’ll have traveled nearly 10 light-years—far enough to
reach many nearby stars. If there were mile markers in space showing the
distance that you’ve traveled, you’d be hitting them more and more quickly, as if
they were closer and closer together—or as if you were traveling much faster
than light. Yet to outside observers, you’d fly past at slightly less than the speed
of light, everything on board apparently frozen in time.
After 4 years of scooting, you’ll have gone 30 light-years, and you’ll be
traveling at 99.95 percent of the speed of light. After 5 years, you’ll be 80 lightyears from where you started, and after 10 years, you’ll have traveled 15,000
light-years, bringing you halfway to the center of the Milky Way. If you
continue accelerating, it would take you less than 20 years of your time to reach
a neighboring galaxy.
If you keep pressing the accelerator for a little over two decades, you’ll find
your vehicle traveling billions of light-years per subjective “year,” carrying you
across a substantial fraction of the observable universe.
In that time, billions of years will have passed back home—so you don’t need
to worry about returning. The Earth will already have been consumed by the Sun
anyway.
But you’ll never reach the farthest galaxies. The universe is expanding, and
thanks to dark energy, the expansion appears to be accelerating.

Traveling at nearly the speed of light may keep you from getting older, but the
rest of the universe continues aging around you. If you travel a billion light-years
at roughly the speed of light, the universe will be a billion years older when you
stop. And since the universe is expanding as it gets older, you’ll find that the
expansion of the universe has carried your destination away from you while you
were traveling toward it.
Because the expansion of the universe is accelerating, there are parts of the
universe you won’t be able to catch up to no matter how far you go. Current
models of the expansion of the universe suggest this limit—known as the
cosmological event horizon—is probably about a third of the way to the edge of
the observable universe.
The Hubble space telescope has zoomed in on seemingly empty areas of the
sky and taken photographs that show seas of dim, distant galaxies. Some of the
larger, brighter galaxies in the photos are within our event horizon, so you could
eventually reach them with your scooter, but most of them are beyond that limit.
No matter how fast you accelerate toward them, the expansion of the universe
will carry them ever farther away.
If you keep holding down the accelerator to chase these unreachable galaxies,
they’ll continue to grow more distant—but you’ll find yourself plunging forward
ever faster in time. After 30 years, the universe will be 10 trillion years old, and
only the smallest and faintest long-lived stars will remain. After 40 years, even
those stars will have burned out, and you’ll find yourself in a dark, cold
universe, lit only by intermittent flashes when the drifting husks of cold, dead
stars happen to collide.
N
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t
e
r
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f
a
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n
d.
CHAPTER 27
How to Be on Time
There are two main ways to arrive somewhere more quickly: traveling faster,
and leaving earlier.
To learn how to travel faster, you can consult chapter 26: How to Get
Somewhere Fast.
Leaving earlier is harder; it involves conscientiousness and realistic planning.
To learn how to be better at those things, you should probably look for a
different book.
If you rule out leaving earlier and traveling faster, then it seems like you’re
stuck. But you do have one more option: alter the flow of time.
This approach isn’t necessarily as implausible as it sounds. When Einstein
was studying the movement of electromagnetic waves through space, he was
puzzled by how Maxwell’s equations seemed to imply that an electromagnetic
wave can never appear stationary relative to any observer. The equations
suggested that you could never catch up to a light wave and see it frozen in place
—no matter how fast you went, you’d measure the light moving past you at the
same number of miles per hour. This led Einstein to realize that something must
be wrong with our idea of “miles” and “hours,” and his theories explained how
time flows differently for different observers depending on how fast they’re
going.
Messing around with time earned Einstein fame, immortality, and a Nobel
Prize,* so maybe it can get you where you’re going on time. (And if not, maybe
you’ll get a Nobel Prize as a consolation.)
“Altering the flow of time” doesn’t necessarily need to involve anything
complicated; the simplest way to do it is to ask everyone to change their clocks.
Many of us already do this twice a year thanks to daylight saving time. After all,
clock time is a social construct. If you can get everyone to agree to turn their
clocks back by an hour, then the time changes, potentially giving you an extra
hour to get where you’re going.
Time zones feel official and permanent, but they’re more freewheeling than
you might think. There’s no international organization that has to approve time
zone boundaries. Instead, every country has the authority to set their own clocks
however they want, whenever they want. If the government of a country wakes
up one morning and decides to move all their clocks back five hours, no one can
stop them.
When a country messes with the flow of time without enough warning, it can
cause some headaches. In March of 2016, the Cabinet of Ministers of Azerbaijan
decided to cancel daylight saving time 10 days before it was scheduled to start.
Software companies had to rush out updates, schedules had to be revised, and
airlines had to decide whether flights should depart at the time on the ticket or an
hour earlier. Heydar Aliyev International Airport just told everyone to arrive 3
hours early for their flights.
Countries usually try to give more than 10 days of warning before changing
their clocks, but they don’t have to. In principle, if you’re running late for an
appointment, you can contact your government and ask them to move the clocks
back.
In the United States, state legislatures can control whether daylight saving
time is observed, but they can’t control when it starts or stops. To gain an extra
hour, you’ll need to contact the federal government.
Federal law currently specifies 9 standard time zones and sets the time in each
relative to Coordinated Universal Time, or UTC—from its French acronym—an
international timekeeping system defined by the International Bureau of Weights
and Measures. Congress can change this law, but you don’t necessarily have to
go through Congress to get your clock adjusted. By law, the secretary of
transportation has the power to unilaterally move territory from one time zone to
another. If you’re in the mainland United States, you can potentially have the
clock moved back by as much as eight hours simply by calling the Department
of Transportation and asking nicely.

The secretary can’t create new time zones, though. If you want to change the
time to something other than the 9 standard values, you’ll need to go through
Congress. But if you can convince them to help you, you can set the time to
whatever you want. In fact, you could—in principle—set the date to whatever
you wanted. You could shift your house, town, or entire country forward by 24
hours . . . or backward by 65 million years.
In 2010, religious radio host Harold Camping predicted that the end of the
world would begin with the Rapture on May 21, 2011, at 6:00 p.m. local time.
Since the apocalypse happened according to local time, this meant that the end
of the world was supposed to begin at the Republic of Kiribati in the Pacific
Ocean, just west of the International Date Line, and sweep westward around the
planet, time zone by time zone.
If some country wants to check whether the world ends at some future date,
they can simply pass a law advancing their clock to, say, 12:00 p.m. on January
1, 3019, and then take a look around. If nothing happens, they can move the
clocks back, and we’ll all know that the next thousand years are safe—at least
from apocalypses that happen in local time.
If you’re unable to persuade the government to change the clocks for you, or
if your appointment is scheduled in UTC, you’re stuck. You can’t get more time
for your appointment unless you can alter UTC itself.
ATOMIC CLOCKS
UTC is based on a network of precise atomic clocks. Atomic clocks measure the
passage of time by precisely measuring the oscillation of cesium atoms using
light. But we know, thanks to Einstein, that the passage of time isn’t constant. In
a strong gravitational field, light—and time itself—slows down. If you put a
large spherical weight next to an atomic clock, the additional gravity will cause
it to tick more slowly.
Unfortunately, you can’t just tamper with one atomic clock. The International
Bureau of Weights and Measures uses measurements from several hundred
atomic clocks spread out around the world and averages them together to
produce a single global time standard. If you wanted to artificially alter time,
you’d have to slow down all those clocks together; if you just messed with one,
they’d quickly notice the outlier.
Let’s suppose you snuck into each atomic clock facility with a ball of lead 1
foot in diameter hidden in your backpack, and left it near the clock. (You’d have
to be pretty strong, since that ball will weigh almost 400 pounds!)
If you managed to hide the ball right next to the atomic clock’s timekeeping
element, it would only slow the clock by about 1 part in 10
24—equivalent to
about a hundred nanoseconds over the next 4 billion years.
A 200-meter-wide ball of lead would be only a little more effective, adding an
extra nanosecond to the clocks every century or so. It would also be impossible
to manufacture and move . . . and pretty difficult to hide.
If UTC is based on atomic clocks, and you can’t mess with atomic clocks,
then it seems like you can’t mess with UTC. But UTC isn’t exactly based on
atomic clocks. It has an irregularity, one which could potentially help give you a
little more time to get to your appointment . . . or, if you leave on time, make
you show up too early.
CHANGING DAY LENGTHS
Our atomic clocks are more precise and regular than the Earth’s spin. We used to
define the length of a second in terms of the Earth’s rotation, but a second whose
length changes over time is inconvenient for physics, engineering, and
timekeeping in general, so in 1967 the length of the second was officially and
permanently frozen to match atomic clocks. A day is supposed to be 24 hours, or
86,400 seconds, but as of the late 2010s the Earth takes about 86,400.001
seconds on average to make one full turn relative to the Sun. In other words, the
Earth is a millisecond too slow. That extra millisecond each day gradually adds
up. After about a thousand days a perfect clock would drift 1 full second out of
sync with the Sun.
The day may only be a few milliseconds too long now, but it isn’t going to
stay that way. Thanks to the Moon, the Earth’s rotation is slowing down.
The Moon’s gravity pulls harder on the nearer parts of the Earth than the
farther parts. As the Earth spins, the water (and, to a lesser extent, the land)
sloshes around slightly to adjust to the shifting force, which we experience as
tides. The Earth spins faster than the Moon orbits, and the gravitational pull
between those sloshing oceans and the Moon create a very slight gravitational
“drag” between the two bodies. This has the effect of pulling the Moon forward
—flinging it into a wider orbit—while also slowing down the Earth.*
LEAP SECONDS
UTC has no time zones or daylight saving, but it’s adjusted every so often—very
slightly—to keep the clocks in sync with the Earth’s rotation. These changes
take the form of leap seconds.
Leap seconds are added by the International Earth Rotation and Reference
Systems Service, which carefully tracks the Earth’s rotation and decides when a
new leap second is needed. The leap second is added right before midnight on
the last day of a month, usually June or December. The second is inserted
between 11:59:59 p.m. and 12:00:00 a.m., and represented as 11:59:60 p.m.
When a leap second is inserted, any event scheduled after that date is pushed
back by 1 second. If your appointment is more than a month or two in the future,
you could potentially gain extra seconds by convincing the International Earth
Rotation and Reference Systems Service that leap seconds are needed.
To get more leap seconds, you need to slow the Earth down faster.
Whenever mass shifts from the equator to the poles, Earth speeds up. The
daily motion of air between the poles and the Equator causes Earth’s speed to
wobble up and down, and over longer periods, redistribution of mass due to
climate cycles, melting ice sheets, and post-glacial rebound all have their own
effects.
That means if you live in a tropical or temperate zone, you can speed up the
Earth simply by walking to one of the poles, and you can slow it down by
walking from the pole back to the equator.
The effect won’t be very large. A single person moving from the pole to the
equator will lengthen the day by less than 1 part in
10,000,000,000,000,000,000,000. It would take a million years for that
discrepancy to add up to a single extra nanosecond. If you want to gain 1 extra
leap second within the next year, you’ll need to move 60 trillion tons of material
from the poles to the Equator.
Even if you use something as dense as gold, that’s over 3,000 cubic
kilometers—enough to wrap the equator in a mile-high wall 150 feet thick.
That’s clearly impossible . . .

. . . unless you can find a magical entity at the North Pole that can produce an
unlimited volume of expensive objects, and magically transport them with
impossible efficiency from the pole all around the world.
CHAPTER 28
How to Dispose of This Book
If you’re done with this book and decide you want to get rid of it, the simplest
thing to do is to give it to someone else.
But maybe you don’t want to give it away. Perhaps you’ve written notes in the
margin that you don’t want anyone to see. Perhaps you simply didn’t like it. Or
perhaps you plan to use the information in the book as part of some kind of
supervillain-style plot, and you’re trying to buy up every copy and destroy them
so no one else can use it to gain an advantage over you.*
If, for whatever reason, you do decide to permanently dispose of this or any
other book, here are a few tips.
AIR DISPOSAL
In a pinch, this book can double as a source of power. The pages contain about 8
megajoules of chemical energy, energy that was originally collected from the
Sun by leaves.
Plants are made of air. The carbon in wood comes from CO2 collected from
the air, which is combined with water (H2O) through photosynthesis. This book
is made from air, water, and sunlight. If the pages are incinerated, the carbon
turns back into CO2 and water, releasing the captured sunlight. When wood, oil,
or paper burns, the heat of the fire is the heat from that sunlight.
Eight megajoules is roughly equal to the energy in a cup of gasoline. If your
car’s fuel economy is 30 miles per gallon on the highway when driving at 55
mph, and you convert it to run on copies of this book instead of gas, it will burn
through 30,000 words per minute, several dozen times faster than the word
consumption rate of a typical human.
OCEAN DISPOSAL
The carbon in a book can also be mixed into water. If the book is incinerated, its
carbon and hydrogen will be converted to CO2 and water. The water vapor will
fall as rain and likely end up in the ocean. Half of the CO2
released into the
atmosphere by combustion will also end up absorbed by the ocean, forming
several septillion molecules of carbonic acid. If it were mixed evenly into the air
and ocean, each cup of seawater and each lungful of air would contain several
thousand molecules from the book.
TIME DISPOSAL
If you set this book down on the ground and walked away, and no one ever
touched it again, what would happen to it?
Depending on the climate in your area, it may not last that long. Humans can’t
eat paper, but the energy stored in cellulose—the same energy released when
you burn it—is appetizing to a wide variety of microorganisms. These organisms
need warmth and high levels of moisture to flourish, so books are usually safe on
your shelf indoors. If you abandon it in a cool, dry cave or shady spot in the
desert, it might last for centuries. But once the book gets wet on a warm day,
organisms—generally fungi—will start to devour the cellulose. The pages will
be digested and eventually mixed into the environment.
If the book is protected from decomposition, its fate may depend on local
geology. If you left it in an area where sediment is being deposited, such as a
low-lying flood plain, it will gradually be buried. If it’s in an area where
sediment is being eroded, like a rocky mountainside, it will almost certainly be
broken down and carried away by the wind and water. Rock erodes at rates
measured in fractions of a millimeter per year, so if this book were made of rock,
it would probably take centuries or millennia to erode away. Since paper is much
softer than rock, it probably won’t take anywhere near that long. The paper will
weather away and disintegrate, and the information printed on it will be lost.
DISPOSAL OF AN INDESTRUCTIBLE OR CURSED
BOOK
It’s technically possible that the copy of this book that you’re reading is
indestructible. Sure, it seems unlikely, but you can’t definitively rule it out
without trying. There’s no nondestructive test for indestructibility.
If you ever get your hands on a book that you want to get rid of but can’t
destroy—either because the paper is too strong, or because of some kind of
Hogwarts library/Ring of Power/Jumanji situation—what should you do? Where
do you put something if you want to get rid of it forever?
We face this problem with nuclear waste. We want to get rid of the stuff, but
there’s no way to destroy it or convert it into a less-dangerous form, because
incinerating or vaporizing radioactive waste doesn’t reduce the radioactivity.
With enough heat, you can destroy anything by breaking its molecules apart into
their constituent atoms. But doing this to radioactive waste doesn’t help—
because the atoms themselves are the problem.
Since we can’t destroy radioactive waste, we generally try to put it somewhere
where it won’t bother us. Collecting it all in a single location makes sense—
there’s not that much waste, volume-wise—so we could just pick a spot, put all
of our waste there, and then seal it off as permanently as possible, monitoring the
site indefinitely, with some kind of warning signs to steer future civilizations
away from digging it up.*
Currently, America’s only long-term permanent underground waste disposal
site is a series of chambers 2,000 feet below the New Mexico desert. The
complex, called the Waste Isolation Pilot Plant, continues to accept a portion of
our nuclear waste, but until a new permanent disposal site is chosen or the WIPP
facility is expanded, we’re solving this problem the way we so often do: by
trying not to think about it and hoping it goes away.
The WIPP tunnels in New Mexico are dug through an ancient layer of rock
salt half a kilometer thick. Salt tunnels are particularly convenient for waste
disposal because the salt “flows” very slowly. If you dig a tunnel through salt
and then abandon it, the tunnel will gradually contract and seal itself off.
To dispose of this book at the WIPP facility, you could dig a cavity off to one
side of a tunnel* and leave this book inside. After a few decades, the cavity will
close up, entombing the text in salt.
There’s another idea for how to get rid of our radioactive waste which,
according to proponents, could be both cheaper and safer than a WIPP-style
facility: dropping it into very deep boreholes.
The WIPP facility is about half a kilometer deep, but boreholes for oil drilling
and geological research* go much deeper. Some reach as far as 10 kilometers
below the surface, down through the surface layers and deep into the underlying
mass of ancient rock that makes up the core of the continent—what geologists
refer to as the crystalline basement.*
In many parts of the world, the rock in the crystalline basement has been
isolated from the surface for billions of years. To dispose of something there, we
could dig a long borehole straight down, drop the waste in, and then seal up the
hole with layers of cement and expanding clay.

SUBDUCTION
Oceanic crust is recycled into the Earth’s mantle through subduction, so people
sometimes suggest putting our nuclear waste in an ocean trench and letting the
Earth dispose of it for us. Unfortunately, subduction is pretty slow. If we lodge
our waste a kilometer deep in a subducting plate, then wait 10,000 years . . .
. . . it will have moved about 300 meters sideways.
SHOOT IT INTO THE SUN
People often suggest shooting our nuclear waste into the Sun, where it will be
disintegrated and will either be carried away by the solar wind or sink to the
Sun’s core. The biggest problem with this idea is that rocket launches fail
sometimes. If you send up 100 rockets full of many tons of radioactive debris,
the odds are pretty good that one of the launches will fail—and it would be hard
to come up with a worse thing to do with nuclear waste than packing it into a
rocket and blowing it up high in the atmosphere.
However, if you’re disposing of a single cursed or indestructible book, then
the Sun seems more attractive as a disposal site. A book only requires a single
launch, which reduces the risk of failure, and if the book is indestructible, then if
the launch fails, you just need to recover it and try again.
A tip for dropping things into the Sun: launching directly to the Sun from
Earth is really difficult—it actually takes more fuel than launching something
out of the Solar System completely. A more efficient way to reach the Sun is to
launch something to the far outer Solar System—possibly with the help of
gravity assists from the planets. When it’s far from the Sun, it will be moving
very slowly, and it will only take a little extra fuel to slow it to a halt—after
which it will fall directly toward the Sun. It takes much longer than a direct
launch, but only requires a fraction of the fuel.
But perhaps you don’t want to destroy this book. Perhaps you want to
preserve it.
HOW TO PRESERVE THIS BOOK
Leaving this book in a borehole or salt mine could in theory preserve it for
millions or perhaps billions of years, if it is not disturbed by tectonic activity,
meddling humans, or hungry microbes. But to really preserve a book, you may
want to remove it from Earth completely.
ESA’s Rosetta spacecraft and Philae lander reached comet 67P/ChuryumovGerasimenko in 2014. The spacecraft carried a nickel-titanium disc etched with
6,000 pages of text in 1,000 different human languages. This disc, constructed
by the Long Now Foundation, is designed to last for millennia. The comet will
likely remain in a stable orbit for millions of years, so if the disc is in a sheltered
location on the surface of the comet, protected from micrometeorites and cosmic
rays, it will probably remain intact and readable for longer than even the longestlived civilization.
Written words are a message to the future. The person reading it is always
further ahead in time than the person writing it. I don’t know what date it is
when you’re reading these words, where you are, or what you’re trying to do.
But wherever you are and whatever problems you’re trying to solve, I hope this
book has helped. There’s a giant, weird world out there. Ideas that sound good
can have terrible consequences, and ideas that sound ridiculous can turn out to
be revolutionary. Sometimes you can figure out which ones work ahead of time,
and sometimes you just have to try them and see what happens.
(But you might want to stand at a safe distance.)
Acknowledgements
A lot of people helped make this book possible.
Many people lent me their expertise and resources. Thank you to Serena
Williams and Alexis Ohanian for their willingness to sacrifice a drone for
science, and to Kate Darling for telling us that it was probably ok to do so.
Thank you to Col. Chris Hadfield for answering the most ridiculous questions I
could think of, and to Katie Mack for warning me not to end the universe. And
thank you to Christopher Night and Nick Murdoch for their help with equations
and measurements.
Thank you to Kathleen Weldon and the Roper Center staff for digging up
strange polling data, and to HuffPost polling editor Ariel Edwards-Levy for
answering my questions about public opinion. Thank you to Anna Romanov and
David Allen for making their undergraduate project available, and to Dr. Reuben
Thomas for sharing his research on friendship. Thank you to Greg Leppert for
helping to arrange the Infrasonata, and thank you to the ants that got into Waldo
Jaquith’s house, which led him to ask me for help building a lava moat.
Thank you to Christina Gleason for molding my text and drawings into the
shape of a book, and providing wise and invaluable advice throughout. Thank
you to Derek for helping to make this whole thing happen, and thank you to Seth
Fishman, Rebecca Gardner, Will Roberts, and the rest of the team at Gernert.
Thank you to my positively heroic editor Courtney Young, and to the rest of
the team at Riverhead, including Kevin Murphy, Helen Yentus, Annie Gottleib,
Ashley Garland, May-Zhee Lim, Jynne Martin, Melissa Solis, Caitlin Noonan,
Gabriel Levinson, Linda Friedner, Grace Han, Claire Vaccaro, Taylor Grant,
Mary Stone, Nora Alice Demick, Kate Stark, and publisher Geoff Kloske.
And thank you to my wife, for teaching me half the stuff in this book and
exploring this big, weird, and exciting world with me.
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24. How to Win an Election
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(Do you think it is generally okay or not okay for people to use their cellphones in the following
situations?) . . . At the movie theater or other places where others are usually quiet
Do you think sending a text message while driving, either on a cell phone or other electronic device,
should be legal or illegal?
(Just off the top of your head, would you say you have a positive or negative image of each of the
following.) How about . . . small business?
Do you think employers should or should not be able to obtain access to employees’ genetic record,
or DNA, without their permission?
As part of the effort to combat terrorism, would you support or oppose . . . creating criminal
penalties for money-laundering involving terrorism?
Right now, a person needs to pass a test and get a license from the government in order to practice a
number of occupations. Some people say this is necessary to guarantee that the public gets good
services. Others say that it just increases the cost of the services. For each of the following, please
tell me if you think government licensing is a good idea, or a bad idea? . . . Doctors
There has been a lot of discussion about what circumstances might justify the United States going to
war again in the future. Do you feel if . . . the United States were invaded . . . it would be worth going
to war again, or not?
Do you think the use of methamphetamines, sometimes known as ‘crystal meth’ should be made
legal, or not?
Please tell me, are you satisfied or not satisfied with your . . . Friends
If a pill were available that made you twice as good looking as you are now, but only half as smart,
would you take it, or not?
(Please tell me if you believe each of the following statements is true or false.) . . . When adults are
supervising children in the water, they should be actively watching constantly, not reading or talking
on the phone.
(Whether you are currently employed or not, think about people on the job, and tell me whether you
think each of the following is okay or not okay.) Do you think it is okay, or not okay, to take more
expensive things like computer or electronic equipment, telephones or other merchandise?
Some people say the following have become more common over the years, and I’d like your opinion
about them. Do you think it is okay, or not okay to pay someone to do a term paper for you?
Let me read you some things some people have said they would like to see happen. Would you like to
see a sharp decline in the number of people who suffer from hunger, or not?
(Let me read you some things some people have said they would like to see happen.) Would you like
to see a decline in terrorism and violence, or not?
Let me read you some things some people have said they would like to see happen. Would you like to
see an end to high unemployment, or not?
Let me read you some things some people have said they would like to see happen. Would you like to
see . . . the elimination of starvation, or not?
(Let me read you some things some people have said they would like to see happen.) Would you like
to see . . . a decline in prejudice . . . happen or not?
(Please tell me whether you believe that any of the following people or items can predict the
future.) . . . The Magic Eight Ball
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A B C D E F G H I J K L M N O P Q R S T U V W X Y
Z
Index
The page numbers in this index refer to the printed version of this book. The link provided will take you to
the beginning of that print page. You may need to scroll forward from that location to find the
corresponding reference on your e-reader.
ablative heat shields, 161
above-ground pools, 10, 12–15
acceleration, 261–70, 262n1, 265n2
accuracy ratios, 225–27, 226n3
Acosta, José de, 33
Adams, John, 110
aging process, 37
air, 21–22, 122–25, 123n2, 204, 282
aircraft carriers, 48–50
airplanes
aircraft carrier landing for, 48–50
cargo airplanes, 88
Colomban Cri-Cri, 55
fuel for, 56
Kennedy airport, 52
landing of, 45–51, 53–56, 58–59
for moving, 86–91, 90n10
ski jump landing for, 48
trim tabs on, 54
water-filled, 204
Aladdin (film), 231
Alaska, 97
aluminum foil, 13
Amazon, 16
animals, 37–38, 60
Aphex Twin, 39–40
Appalachian Trail, 141, 143–44
Approximate Analytical Investigation of Projectile Motion (Chudinov), 112n3
Armstrong, Neil, 53
astronomy, 217–22, 277–78, 278n2
Atchison, Justin, 164
athleticism, 1–9, 6n4
atomic clocks, 276–77
Australia, 25, 52–53
Azerbaijan, 273
bad ideas, viii—ix
balloons, 75–76
Barcelona, 44
Basilica of Our Lady of Peace, 254
basketball, 1
bats, 37
Beauty and the Beast (film), 231
bedrock, 95–98
Beethoven, 41
Betz’s law, 178
bicycles, 64, 66, 209
Bingham Canyon copper mine, 32
birthdays, 194, 230–39
BLS. See Bureau of Labor Statistics
boiling, of water, 69–73
Boll, Uwe, 140, 140n2
Bolt, Usain, 138–40
Boncompagni, Ugo, 140, 140n4
Boston, 75
bottled water, 16–18
boundaries, 95–98, 167
Bureau of Labor Statistics (BLS), 28
butterflies, 197–200
butterfly effect, 131
California, 52, 85, 97, 173, 249
Camping, Harold, 275
Canada, 74, 96, 241
carbon dating, 236–39
cargo airplanes, 88
Carpe Jugulum (Pratchett), 192–93
cars, 65–66
Casey, Bob, 242–43, 243nn4–5, 246
categorical imperatives, 192
cats, 37
channels, in rivers, 62–63
chaos theory, 131, 131n3
charging, of phones, 201–8
chasing, 100
cheating, 2, 5
cheese, 14–15
cheetahs, 223–24
chicken pox, 231–32
China, 40, 254
Christmas, 248
Chudinov, Peter, 112n3
Chunnel, 55
climate change, 23–24
clouds, 132–35
coal, 172
cockpit doorways, 51
Cohen, Michael P., 249
Cold War, 17–18, 40, 87, 236
collisions, 189–90
Colomban Cri-Cri (airplane), 55
comets, 289
computers, 130–32, 195–200
construction cranes, 55
cooling, 106–8
The Core (film), 51–52
cosmological event horizon, 270
Côte d’Ivoire, 254
Craigslist, 58
cropping, of images, 214–15
crossing, of rivers. See rivers
crystalline basement, 286–87, 286n5
Cullen Earthquake Act, 97
Curiosity (rover), viii
Currey, Donald, 249
curses, 284–87
dams, 203
daredevils, 65
dark energy, 269
Darling, Kate, 229
delivery drones, 59
Department of Energy (DOE), 172
destinations, 136
digging holes, 11, 27–33, 78
Disney, 231
disposal, 281–90, 285n2
DNA, 199
DOE. See Department of Energy
dogs, 37
dog walking, 194
drag force, 84, 112–15, 112n3, 122–25, 123n2
dragonflies, 87
drones, 59, 197, 223–29
drowning, 62
Dubai, 254
Dwyer, Budd, 243
Earth, 277–80, 287
earthquakes
in California, 97
infrasound of, 40
tectonic plates in, 174–75
echoes, 37
economics
of excavations, 30
of heat, 106
of mailing, 159
of power, 175
of promotions, 166n5
Edwards Air Force Base, 52
The Effect of Nuclear Explosions on Commercially Packaged Beverages (government report), 17–18, 18n4
Egan, John, 251
Einstein, Albert, 272–73, 272n1
elections, 240–47
electricity, 201–3, 206
electronic devices, 201–8
elephants, 38
energy. See also power
dark energy, 269
electrical energy, 206
fuel for, 68
National Renewable Energy Laboratory, 177
potential energy, 205
for steam, 70
vacuum energy, 179–80
Enevoldson, Einar, 7–8
England, 55
escalators, 205–9
Estes, Ron, 241
Estes, Ron M., 241
excavations, 30–32
expertise, 45
exploration, viii. See also space
eyesight, 211
FAA. See Federal Aviation Administration
fake photography, 212
farms, 46–47
fault lines, 97
Federal Aviation Administration (FAA), 169
field of view, 211–13, 216–17
Fiji water, 16
files (computer), 195–200
fire, 205
FiveThirtyEight, 244
flatbed trucks, 83–85, 84nn6–7
Florida, 255
football, 117–26
fording. See rivers
forecasting, 127–35
forests, 248, 248n1. See also trees
formulas
with air resistance, 122–25
for collisions, 189–90
with drag, 84, 112, 122–25
with friction, 80, 146–47
for hoop stress, 12
for hovering, 90
for jumping, 64
for photography, 218–19
for physics, 4
for pool wall thickness, 14
for power, 171, 175–76
for ratios, 223–24
for snowflakes, 152
for throwing, 111–13, 112nn2–3
for water depth, 13
for water freezing, 68
for weight, 78–79
Fosset, Steve, 7–8
fossil fuels, 172–73, 182, 239n6
foundations, for houses, 82–83, 91–92, 94–98
France, 55
freezing, of water, 67–69
friction, 79–81, 146–51
Friends (TV show), 235–36
friendships
formation of, 189–93
with neighbors, 144
fuel
for airplanes, 56
buried, 172–73
for energy, 68
Gardiners Island, 28–29
generators, 206–9
geothermal power, 173, 182
Germany, 254
Gerwen, Michael van, 226
The Geysers, 174
Google, 107
government, 274–75
gravity
acceleration and, 261
in space, 288
time and, 276
water and, 171–72
Greece, 2n4
Greenland, 25
El Guerrouj, Hicham, 138–40
Guinness World Records, 251
Hadfield, Chris, 60
on airplanes, 45–51, 53–56, 58–59
in cars, 65
on space shuttles, 51–53, 56–58
Harlan, Tom, 250n2
hearing, 36–41
heat, 103–4, 106, 159–62, 159n1
Hedberg, Mitch, 208
helicopters, 86–88
highways, 259
hiking, 141, 143–44
Historia Natural y Moral de las Indias (Acosta), 33
Holloman Air Force Base, 265
hoop stress, 12
horsepower, 122–25
houses, 59
foundations for, 82–83, 91–92, 94–98
lava moats for, 101–8
moving of, 82–85, 84n5, 85nn6–7
power for, 168–72, 176–79, 181–88
hovering, 89–91
hydropower, 171–72, 182, 203–4
Hyperion, 252–53
ice
ice machines, 68
ice skating, 147–48
science of, 24–25
ideas
bad ideas, viii—ix
plausibility of, viii
images
cropping of, 214–15
resolution of, 210–11
indestructibility, 284–87
industrial shredders, 18–19
Infrasonata, 43
infrasound, 38–39
in-ground pools, 10–12
International Boundary Commission, 96
International Bureau of Weights and Measures, 276
International Earth Rotation and Reference Systems Service, 278–79
International Space Station (ISS), 57–58, 157–58, 164–65
internet
quizzes on, 230–31
viral videos on, 23, 66–67
internet water, 16
iPhone X, 213
irrigation, 25–26
Isinbayeva, Yelena, 2n4
ISS. See International Space Station
Jefferson, Thomas, 110
jellyfish, 108
Jepsen, Carly Rae, 114
Joannou, Andrea, 97
Joannou v. City of Rancho Palos Verdes, 97
jumping
athleticism of, 1–9, 6n4
over rivers, 63–65
Jupiter, 219–21
Jurassic Park (film), 131n3
Kansas river, 69–72
Kant, Immanuel, 192
Kennedy airport, 52
Kennedy Space Center, 255
Kidd, William, 28–29
kites, 73–75, 75n9
Knievel, Evel, 65, 67
Knoll, Catherine, 242–43, 243nn3
knowledge, ix
Kouros, Yiannis, 141–42
Krzywinski, Martin, 143
land
landslides, 97–98
water from, 25–26
landing
of airplanes, 45–51, 53–56, 58–59
of space shuttles, 51–53, 56–58
lava moats, 101–8
Lavillenie, Renaud, 4
lawn darts, 224, 224n1
leap seconds, 278–80
learning
knowledge and, ix
memorization and, 35–36
legal cases
California v. Carney, 85
Joannou v. City of Rancho Palos Verdes, 97
Theriault v. Murray, 98
lifehacks, 205
Limited Nuclear Test Ban Treaty, 236
The Lion King (film), 231
listening
for echoes, 37
for explosions, 42
to friends, 192–93
to music, 44, 231
for noises, 40–41
The Little Mermaid (film), 231
López-Morillas, Frances, 33
Lord of the Rings (films), 122
Lorenz, Edward, 131
Los Angeles, 52
Los Angeles Times, 251
Mack, Katie, 179–80
mailing, 157–61, 164–67
Maine, 98
Mars, viii, 181–88
matter, 67–73
Maxwell, James, 272–73
mean free path, 189–90
melting, 102–4
memorization, 35–36
Methuselah, 250
mice, 37
microbaroms, 41
MicroSD cards, 196–97, 199
Mir space station, 165–66
moisture, 22
momentum, 122, 124n2
Monarch Watch, 199
the Moon, 211–15, 217–19
Mooney, Jay, 34n1
motorcycles, 65–66, 223–24
motor homes, 85
movies, 231
moving
airplanes for, 86–91, 90n10
of houses, 82–85, 84n5, 85nn6–7
packing for, 77–82, 79n1, 81n3
unpacking after, 92–93
music
listening to, 44, 231
musical notation, 35
pianos, 34–43
names, 233–36
NASA, viii, 88, 211, 255–56. See also space
National Association of Conservation Districts, 170–71
National Renewable Energy Laboratory, 177
natural gas, 172
neighbors
boundaries between, 97–98
friendships with, 144
lava moats and, 101–8
stealing from, 19
Neumann, John von, 130
New Kids on the Block, 231, 238
New Mexico
Holloman Air Force Base in, 265
WIPP in, 285–86
New Zealand, 25
Niagara Falls, 73–75
noises, 40–41
Nova Scotia, 29–31
nuclear weapons, 17–18, 18n4, 40, 236
Oak Island, 29–31
Obama, Barack, 114
occultation, 221–22
ocean disposal, 282
Office of Energy Efficiency and Renewable Energy, 68
Ohanian, Alexis, 227–28
oil, 172
open-pit mines, 32
opinion polls, 244–46
Outer Space Treaty, 169
packages. See mailing
packing, for moving, 77–82, 79n1, 81n3
Panama Canal, 33, 256
paragliding, 7
parallel parking, 84n6
Parker, Dorothy, 127
Peck, Mason, 164
Pennsylvania, 242–43, 243nn4–5, 246
Perkins, Samuel, 75, 75n9
persistence forecasting, 130
Phobos, 182–87
phones, 201–8, 215–22
photography
science of, 210–15
selfies, 215–22
physics, 4n2
of acceleration, 261–70, 262n1, 265n2
of astronomy, 277–78, 278n2
Betz’s law, 178
of cooling, 106–8
of drag, 84, 112–15, 122–25, 123n2
of earthquakes, 97
formulas for, 4
of friction, 79–81, 146–51
of helicopters, 86–88
of houses, 82, 91–92
on Mars, 181–88
mean free path, 189–90
of melting, 102–4
of momentum, 122
of running, 139–41
of skiing, 145–50, 146n3, 149n4
slope, 149–50
of sound, 38–41
of throwing, 111–15
of thrust, 88–91, 257
of time, 276–77
of trains, 265
of walking, 141–43
of weight, 78–79, 79n2
pianos, 34–43
piezo-electric effect, 42
pirate treasure, 28–29
places, going to, 136
plants, 170–71
plausibility, viii
plutonium, 186n3
Pokémon, 231
polar night jet, 7–9, 8n9
pole vaulting, 2–4
pools
above-ground pools, 10, 12–15
in-ground pools, 10–12
making water for, 20
on Mars, 188
water sources for, 15–19, 21–26
potential energy, 205
power
of butterflies, 198–99
for electronic devices, 201–8
horsepower, 122–25
for houses, 168–72, 176–79, 181–88
sources of, 170–75
units of, 176n1
from vacuum decay, 180
Pratchett, Terry, 192–93
predictions, 127–35
preservation, 289–90
presidents, of US, 109–10, 114–16
Prometheus, 249–50
promotions, 165–66, 166n5
punctuality, 272–80, 279n2
quizzes, on internet, 230–31
radioactive waste, 284–88, 285n2
rain, 21, 171–72
range to error ratio, 225
Rappahannock River, 109, 115
ratios, 223–27, 226n3
rats, 37
redwood trees, 253
rivers
balloons for, 75–76
jumping over, 63–65
kites and, 73–75, 75n9
running on, 66–67, 66n2
science of, 61–63, 67–73
Snake River Canyon, 65
robots, 229
rocs, 60
Rogers Dry Lake, 52
roller skating, 156
Roper Center, 244–46
Rosetta (spacecraft), 289
rotary woofers, 42
running, 3–4, 139–41
Russia
Mir space station for, 165–66
Russian Orlan spacesuits, 57
walking in, 143
RVs, 85
Salton Sea, 26
satellites, 166–67
SCA promotions, 165–66, 166n5
scars, 232–33
SCAs. See Shuttle Carrier Aircrafts
Schulman, Edmund, 249
science. See also physics
astronomy, 217–22
of balloons, 75–76
of bedrock, 95–98
carbon dating, 236–39
of cars, 65
climate change, 23–24
of clouds, 132–35
of crystalline basement, 286–87, 286n5
of energy, 68, 70
of hearing, 36–41
of heat, 103–4, 159–62, 159n1
horsepower, 122–25
of hovering, 89–91
of ice, 24–25
leap seconds in, 278–80
on Mars, 181–88
of matter, 67–73
of moisture, 22
of photography, 210–15
of power sources, 170–75
of rain, 21
of rivers, 61–63, 67–73
of snow, 149–55
of the sun, 176–77
of tea kettles, 68–73, 70n4, 72n6
of tectonic plates, 95–96, 174–75
of time, 276–80, 282
of water, 20
of weather, 127–35
scooters, 261–64, 267–71
seas
Salton Sea, 26
seawalls, 32, 32n6
water from, 23–25
selfies, 214–22
shovels, 27–28
Shuttle Carrier Aircrafts (SCAs), 57–58
Sioux City, 51
siphons, 19
skiing, 5, 48, 145–51, 146n3, 149n4, 153–56
skylines, 212
skyscrapers, 254
slope, 149–50
small pox, 232–33
Snake River Canyon, 65
snow, 149–55
snowmobiles, 66
Sociological Perspectives (Thomas), 191
sound, physics of, 38–41
Soyuz (spacecraft), 59
space
gravity in, 288
ISS, 57–58, 157–58, 164–65
Kennedy Space Center, 255
Mir space station, 165–66
Outer Space Treaty, 169
for preservation, 289
shuttles, 51–53, 56–58, 88
SpaceX, 164
travel, 157–67, 266–71
vacuums in, 179–80
Spain, 44
sports equipment, 224–29
Springsteen, Bruce, 44
sprinters, 6
stealing, 19
steam, 70
Stevenson, Robert Louis, 29
Stratosphere Giant, 253
subduction zones, 287
submarines, 51
the Sun, 176–77, 182, 211, 288
supermoons, 211–12
surface tension, 66–67, 66n2
Swank, Hillary, 51–52
Syracuse University Lava Project, 102
Taco Bell, 165–66, 166n5
tag (game), 137–44, 151
tea kettles, 68–73, 70n4, 72n6
tectonic plates, 95–96, 174–75
teeth, 236–39
telescopes, 221, 221n2, 270
terminal velocity, 6–7, 112–13
Theriault v. Murray, 98
Thomas, Reuben J., 191
throwing, 109–16, 119–20, 151
thrust, 88–91, 257
time
science of, 276–80, 282
zones, 273–76
tools
shovels, 27–28
vacuums as, 31–32
weapons as, 16–17
tornadoes, 100
Toy Story (film), 231
trains
for airplane landings, 50
physics of, 265
travel
in space, 157–67, 266–71
speed of, 260–65, 262n1, 265n2
treasure, 28–29, 28–31
Treasure Island (Stevenson), 29
trees
decoration of, 151
displaying of, 253–58
selection of, 248–53
trim tabs, 54
trucks, 22, 80–85, 84nn6–7
turbines
for escalators, 206–08
for water, 203–4
for wind, 177–79, 184–87, 204
TV shows, 231, 235–36
Twain, Mark, 127
ultrasound, 37
Union of Soviet Socialist Republics (USSR), 236. See also Russia
United States (US)
Alaska, 97
Appalachian Trail, 141, 143–44
Bingham Canyon copper mine, 32
BLS, 28
California, 52, 85, 97, 173, 249
Christmas in, 248
Cold War for, 17–18, 87
DOE, 172
Edwards Air Force Base, 52
FAA, 169
government in, 274–75
Holloman Air Force Base in, 265
houses in, 169
International Boundary Commission for, 96
National Renewable Energy Laboratory, 177
New Mexico, 265, 285–86
Office of Energy Efficiency and Renewable Energy in, 68
passage of time in, 274
Pennsylvania, 242–43, 243nn4–5, 246
presidents of, 109–10, 114–16
redwood trees in, 253
research in, 236
Snake River Canyon, 65
tornadoes in, 100
Utah, 32
White Mountains in, 249
WIPP in, 285–86
the Universe, 267–71
unpacking, after moving, 92–93
uranium, 172
US. See United States
Usnea barbata, 140, 140n5
USSR. See Union of Soviet Socialist Republics
Utah, 32
vaccines, 232–33, 233n2
vacuums, 31–32, 179–80
Vatican City, 253
Venezuela, 167
Venus, 219–21
videos, 66–67
viral videos, 23, 66–67
voting, 240–47
walking
dog walking, 194
physics of, 141–43
walls, 13
Walsh, Homan, 74
Washington, George, 109–10, 115–16
Waste Isolation Pilot Plant (WIPP), 285–86
water
air and, 21–22, 204
boiling of, 69–73
bottled water, 16–18
freezing of, 67–69
gravity and, 171–72
industrial shredders for, 18–19
Internet water, 16
from land, 25–26
making, 20
on Mars, 182
from neighbors, 19
for pools, 15–19, 21–26
running on, 65–66, 66n2
science of, 20
from sea, 23–25
turbines for, 203–4
weapons
nuclear weapons, 17–18, 18n4, 40, 236
pole vaulting equipment as, 2
as tools, 16–17
weather, 127–35
weight, 78–79, 79n2, 111–15
Weldon, Kathleen, 244
wheels, 206–8, 206n4
White Mountains, 249
wide-angle selfies, 215–16
wide load permits, 84n7, 86
Wilde, Oscar, 127
Williams, Serena, 75, 227–28
wind
on Mars, 182
turbines for, 177–79, 184–87
wingsuits, 7–9, 8n9
WIPP. See Waste Isolation Pilot Plant
The Wizard of Oz (film), 59
World Chase Tag, 137
world records
for holes, 33
for jumping, 4, 6n4
for trees, 251
YouTube, 66
Znoneofthe, Above, 241
zooming, 213
A B C D E F G H I J K L M N O P Q R S T U V W X Y
Z

About the Author
Randall Munroe is the author of the #1 New York Times bestsellers What If? and
Thing Explainer, the science question-and-answer blog What If, and the popular
webcomic xkcd. A former NASA roboticist, he left the agency in 2006 to draw
comics on the internet full-time. He lives in Massachusetts.
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*
O
r
a
l
t
e
r
n
a
t
i
v
e
l
y
,
f
o
r
t
h
e
n
i
n
e
t
i
e
s
k
i
d
s
o
u
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t
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e
r
e
,
N
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c
k
e
l
o
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o
n
®
M
o
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n
S
h
o
e
s
®
™
* Physics offers another interesting piece of trivia about pole
vault world records. The downward pull of Earth’s gravity
varies from place to place, both because the shape of the Earth
affects its gravity and because the spinning motion “flings”
things outward. These effects are small in the grand scheme
of things, but the variation from place to place can be as much
as 0.7%. That’s not enough to notice when you’re walking
around, but it’s enough so that when you buy a scale, you may
need to calibrate it, since gravity at the factory could be
slightly different from gravity at your house.
The varying pull of gravity is enough to affect pole vault
records. In June 2004, Yelena Isinbayeva set the then
women’s pole vault world record, with a height of 4.87m. She
set this record in Gateshead, England. A week later, Svetlana
Feofanova broke her record by 1 cm, jumping 4.88m.
However, Feofanova set this record in Heraklion, Greece,
where the pull of gravity is slightly weaker. The difference is
just enough that, if she wanted, Isinbayeva could argue that
Feofanova only broke the record because of the weaker
gravity, and her Gateshead jump was the more impressive
one.
Isinbayeva apparently decided not to make this complicated
physics argument, and instead went for a simpler response: a
few weeks later, she broke Feofanova’s record, again jumping
in the stronger British gravity. As of 2017, she still holds the
women’s record.
*
A
t
l
e
a
s
t
,
I
a
s
s
u
m
e
y
o
u
w
o
u
l
d. I
t
’
s
p
o
s
s
i
b
l
e
n
o
o
n
e
’
s
e
v
e
r
t
r
i
e
d.
* As of this writing, there’s no world record for the highest
high jump by an athlete wearing a Victorian hoop skirt, but if
there were, it would probably be lower than the regular
record.
*
W
e
’
r
e
c
h
e
a
t
i
n
g
,
b
u
t
w
e
’
r
e
n
o
t
c
h
e
a
t
i
n
g.
* At least, from a physics point of view. It probably matters a
lot to you personally.
* You’d also have to convince the judges to hold the
competition near the edge of a cliff, which might be difficult.
* The polar night jet is a high-altitude wind stream that exists
near the Arctic and Antarctic at certain times of year. Not to
be confused with The Polar Night Jet, a heartwarming
children’s picture book about a child who visits Santa one
night by flying to the North Pole in a magical stealth bomber.
* You’ll need to pressurize the sailplane cabin around you,
but that shouldn’t be too hard, right? Just make the fiberglass
shell airtight, but add a hose for breathing. When you get a
few miles up and the air pressure really starts dropping, just
pinch off the hose to seal yourself in. You might be up there
for a while, so try to make the cabin big enough that you
won’t run out of air.
* We forgot doors, so when you land, call a friend to come
break open your sailplane with a hammer.
* In practice, it will probably burst before that point, thanks to
irregularities in the materials and their particular “yield
curves,
” but we can use simple tensile strength as an
approximation.
*
T
h
e
d
r
i
n
k
s
,
n
o
t
t
h
e
s
t
o
r
e
s.
* They focus in particular on beer, which seems like it would
be less than ideal in a post-nuclear-attack recovery scenario,
and it makes you wonder whether the entire test program was
hastily arranged as a cover story when someone was caught
charging drinks to their work account.
* In an example of oddly excessive attention to detail, the
bottles on the ground were placed at a variety of carefully
measured angles relative to ground zero—some lying with the
top or bottom end pointed toward ground zero, some lying at
45° angles, and some upright. Perhaps they wanted to see
which way you should store your bottles relative to the city
center to maximize the chance they’d survive a nuclear attack.
*
I
h
o
p
e
t
h
i
s
i
s
a
e
u
p
h
e
m
i
s
m
f
o
r
“
f
r
i
e
n
d
s
o
f
o
u
r
s.”
*
A
s
o
f
2
0
1
9.
* This is just an average—the total amount of water per
square meter varies from almost nothing, in cold air over
deserts, to up to 20 gallons per square meter of land on a
humid day in the tropics.
* [Citation needed]
* Search for Pantai Remis landslide.
*
O
r
p
u
t
i
n
t
h
e
p
l
u
g
,
I
g
u
e
s
s.
* Pirate.
*
P
i
r
a
c
y.
*
P
i
r
a
t
e
s
d
o
a
l
o
t
o
f
t
h
i
n
g
s
s
i
n
g
l
e
-
h
a
n
d
e
d
l
y.
*
F
o
r
c
o
n
t
e
x
t
,
I
’
m
w
r
i
t
i
n
g
t
h
i
s
i
n
t
h
e
y
e
a
r
1
7
3
1.
* Note to any far-future historians who found this page and
are trying to figure out what year it was really written: That
was just a joke. I’m writing this in 2044 CE. from my airship
circling the South Pole. I’m so glad this manuscript survived
to serve as your Rosetta Stone, and I promise to take this
responsibility seriously. By the way: here in the year 2044, we
all worship dogs, fear clouds, and eat nothing but honey on
the day of a full moon.
* A seawall is just a reverse above-ground pool, so you can
use the calculation from chapter 2: How to Throw a Pool
Party to figure out the engineering. Just use compressive
strength instead of tensile strength in the equation.
* Thank you to Jay Mooney, whose question prompted this
chapter.
*
W
h
i
c
h
m
a
k
e
s
y
o
u
w
o
n
d
e
r
w
h
y
w
e
n
e
e
d
a
l
l
t
h
o
s
e
o
t
h
e
r
i
n
s
t
r
u
m
e
n
t
s.
* (But fortunately for our piano tuner)
* For instructions on how to play the piano underwater, see
How To 2: How to Do a Bunch More Stuff, If You’re Still
Alive after Following the Instructions in the First Book.
* I really hope we don’t have to revise this paragraph before
the next printing.
* If you were trying to stay above the water’s surface by
running, it would actually make more sense to run in place, so
your feet would be moving quickly relative to the water’s
surface. A lightweight barefoot water skier with large feet can
stay above the surface at only 30 mph, which is about 5 mph
faster than the running speed of the fastest sprinters. So
staying above water by running in place is probably
impossible, but we won’t know for sure until someone takes a
champion sprinter—one with a small body and large feet—
and lowers them slowly into a pool of water as they run in
place. Good luck with that grant application!
*
I
t
’
s
e
n
o
u
g
h
t
o
g
o
b
a
c
k
t
o
t
h
e
f
u
t
u
r
e
7
1
t
i
m
e
s.
* Most electric kettles—like most hair dryers—are limited to
1875 watts, because if they drew any higher, they wouldn’t be
able to be safely plugged into US household outlets rated at
15 amperes (amps, A).
* Ten megakettles.
* Once the kettles are removed, the crater they left behind will
be filled in by the river, forming a temporary kettle-hole pond.
(Thank you to the approximately four glacial hydrologists out
there who laughed at that.)
* For some reason.
* The July 13, 1848 issue of The Buffalo Commercial
Advertiser contains the headline “Incidents at the Falls,
”
under which appeared a breaking news story announcing that
a very cute bird—a phoebe—has nested near the paddle wheel
of the Maid of the Mist Falls tourist steamship, and has
successfully raised and fledged a family of chicks several
years in a row. I love old newspapers, and wish I got breaking
news alerts on my phone about that kind of thing.
* The biplane wing was also damaged, but the pilot was able
to land safely.
* You also may need to saw your refrigerator into pieces to
make it light enough to carry.
* On average. You’ll probably be able to walk faster on the
return trip, since you’ll be walking without a load.
* Yes, there are elite tug-of-war teams. The sport is much
more dangerous than is commonly realized; see whatif.xkcd.com/127 for the horrifying details.
*
O
r
t
o
h
i
r
e
m
o
v
e
r
s
t
o
p
a
c
k
t
h
e
h
o
u
s
e
f
o
r
y
o
u.
* If there are no hurricane ties, you might be able to save
yourself some effort—if you wait long enough, a hurricane or
tornado might come along and move the house for you.
* For one thing, parallel parking is a huge pain. On the other
hand, when you try to merge, people will probably be more
likely to yield to you.
* In order to transport a house on the highway, you generally
need to obtain special “wide load” permits, and if you’re
moving your house based on instructions in a book by a
cartoonist, it seems like a safe bet that you haven’t applied for
those.
*
W
h
i
c
h
r
e
a
l
l
y
s
h
o
u
l
d
h
a
v
e
g
o
n
e
b
y
t
h
e
c
o
d
e
n
a
m
e
H
E
L
I
C
E
N
T
I
P
E
D
E.
* If you do live at the end of the runway, I would love to
know about your homeowner’s insurance policy, and whether
your comprehensive auto insurance covers collisions with
aircraft.
* If you do run out of fuel mid-flight and start to fall, please
consult chapter 5: How to Make an Emergency Landing, and
skip to the section “How to Land a Falling House.”
*
S
e
e
c
h
a
p
t
e
r
3: H
o
w
t
o
D
i
g
a
H
o
l
e.
*
S
e
e
c
h
a
p
t
e
r
1
6: H
o
w
t
o
P
o
w
e
r
Y
o
u
r
H
o
u
s
e
(
o
n
E
a
r
t
h
).
* Your lava moat might help with keeping ants out, but it
could also attract lava crickets. These insects, Caconemobius
fori, live on or near recently cooled lava flows. Not much is
known about them, since they are—as you might imagine—
challenging animals to study.
* Elementary physics classes commonly analyze motion
under constant force, and students may see those equations so
often they learn them by heart. The equations of motion under
constant power, with different exponents and coefficients, are
a little more obscure. They’re outlined in a 1930 paper by
Lloyd W. Taylor of Oberlin College titled The Laws of
Motion Under Constant Power.
* Note: The formula now underestimates a baseball player’s
pitching speed as being only about 80 mph, but it gives
otherwise reasonable results. The discrepancy might be
explained by the fact that baseball players spring forward,
giving them some forward speed at the start and stretching
their pitch over a longer distance, but it’s a very simple model
—we don’t want to go too far trying to explain or correct
every deviation.
* This equation is based on approximations from the 2017
paper Approximate Analytical Investigation of Projectile
Motion in a Medium with Quadratic Drag Force by Peter
Chudinov. If the projectile is dense or the atmosphere is thin,
it’s equivalent to the standard range equation for an object
launched at a 45° angle (range = v
2
/ g), but at higher speeds,
where air resistance is a bigger factor, it gives shorter
distances.
* The NFL rules actually do contain the word “horse,
” but
only in reference to a move called a “horse-collar tackle.”
* If you’ve taken some physics classes and you stare at this
diagram long enough, you might start to wonder what the ½ is
doing in the drag equation. Since the drag coefficient is a
unitless, arbitrary scale factor, the ½ could be eliminated just
by doubling all the drag coefficients. Sports physicist John
Eric Goff has pointed out that if you derive the equation by
thinking about the momentum carried by the incoming air
molecules, it seems like a factor of 1—or possibly 2—would
be more natural than ½. However, if you think of drag in
terms of the kinetic energy of the incoming air, then carrying
over the ½ from the kinetic energy equation makes more
sense. Physicists tend to explain it this way—by saying the
drag equation represents the “dynamic pressure” of the
incoming air—but not every authority agrees. Frank White’s
Fluid Mechanics textbook simply calls the factor of ½ a
“traditional tribute to Euler and Bernoulli.”
* This horse-drag equation doesn’t have a common name in
physics, and honestly it would be pretty weird if it did.
* We humans are good at being surprised by predictable
changes. Every time I see a friend with their baby, I feel the
urge to comment,
“Oh, you’ve grown since I last saw you!”
Apparently some part of me expects babies to stay the same
size or get smaller over time.
*
A
s
o
f
2
0
1
9.
* And, according to Jurassic Park, somehow led to a bunch
of dinosaurs eating people.
* If you want to annoy a physicist, mention to them that the SI
unit for “seconds per hour” is “radians.”
* “When it is evening, ye say,
‘It will be fair weather: for the
sky is red.’ And in the morning,
‘It will be foul weather today:
for the sky is red and lowering.’”– Matthew 16:2–3.
* 400 meters is just barely long enough to use up a sprinter’s
anaerobic reserves and require some aerobic energy.
* A horror filmmaker
* The birth name of Pope Gregory XIII
*
A
s
p
e
c
i
e
s
o
f
l
i
c
h
e
n
* Depending on road closures and border procedures, you
may also need to take a ferry on Lake Nubia/Lake Nasser in
order to cross the Egypt/Sudan border.
*
I
r
o
n
i
c
a
l
l
y
,
i
t
’
s
n
e
v
e
r
r
e
a
l
l
y
g
a
i
n
e
d
t
r
a
c
t
i
o
n.
*
T
h
e
s
e
c
o
n
d
2
i
s
a
f
o
o
t
n
o
t
e
,
n
o
t
a
s
u
p
e
r
s
c
r
i
p
t.
* Bicycles have wheels, but they’re still subject to friction—
the wheels just move the location of some of the friction from
the ground to the bearings of the axle.
* Objects have a lower coefficient of friction when they start
moving. This is the reason why, when you slip on a patch of
ice, your feet go out from under you so abruptly. As soon as
your shoes start to move, they lose their grip completely.
* Why don’t spacecraft slow down using rockets, then enter
the atmosphere at a low speed, to avoid the need for a bulky
heat shield? The answer is simple: it would take way too
much fuel. The spacecraft that use rockets for landing, like the
Curiosity rover or SpaceX’s reusable launchers, do most of
their decelerating using atmospheric drag, and only use
rockets for the last bit of the landing.
Getting a spacecraft going against gravity fast enough to get
into orbit takes dozens of times the spacecraft’s own weight in
fuel, which is why rockets are so big. Slowing down would
take roughly the same amount. Which means that instead of
launching a 1-ton spacecraft to orbit using 20 tons of fuel,
you’d need to launch a 1-ton spacecraft and 20 tons of fuel to
slow it back down. But now instead of a 1-ton spacecraft,
you’re effectively launching a 21-ton spacecraft, which means
you’ll need 420 tons of fuel. Compared to 420 tons of fuel, a
100-pound heat shield is a way more efficient solution.
*
I
t
’
s
n
o
t
a
s
b
a
d
a
s
i
t
s
o
u
n
d
s. O
k
,
i
t
w
a
s
r
o
u
g
h
l
y
a
s
b
a
d
a
s
i
t
s
o
u
n
d
s.
* On the other hand, this was the mid-20th century—you’d
think if they were so worried about radioactive particles in the
atmosphere, perhaps they should have considered not setting
off so many nuclear bombs. But what do I know; I wasn’t
there.
* The Apollo command modules landed in the ocean. Soyuz
spacecraft land in a large open area in Kazakhstan where
they’re not likely to hit anything.
* Was Taco Bell serious about this? Well, sort of. They
bought a $10 million insurance policy to cover the demand for
free tacos in the unlikely event of a “win.” This policy was
purchased from SCA Promotions, a company which provides
coverage for promotional contest wins. When a company
wants to promise a large prize to anyone who completes a
difficult task, they pay a fixed amount to SCA Promotions,
and SCA pays out if they succeed. However, the premiums
Taco Bell paid for the policy probably weren’t too high—
since they placed the target near the Australian coast,
thousands of miles west of the reentry path.
* The gold discs were part of a science experiment. The
science experiment was part of the cover story, in case anyone
asked what the satellite was doing up there.
* A note on units: “1.38 kilowatts” isn’t a per-year
measurement—it’s just the rate at which an average American
consumes electricity, averaged over time. People are used to
measuring electricity consumption in kilowatt-hours (the
energy to supply one kilowatt for one hour) since that’s how
it’s priced and sold. This is perfectly valid, but it’s a little
strange from a physics point of view. After all, the average
could just be expressed in “kilowatts.” It’s like saying the
width of a road is “100,000 square feet per mile” instead of
saying that it’s 20 feet wide.
*
I
f
y
o
u
d
o
,
y
o
u
w
o
n
’
t
f
o
r
l
o
n
g.
*
F
o
r
m
o
r
e
o
n
t
h
i
s
,
s
e
e
c
h
a
p
t
e
r
2
7: H
o
w
t
o
B
e
o
n
T
i
m
e.
* Since the speed of sound on Mars is lower, if you tried to
talk, your voice would sound significantly deeper.
* It doesn’t come close to plutonium, though, which produces
hundreds of watts of heat per kilogram for many decades. But
plutonium is hard to come by in large amounts. The Curiosity
rover—possibly your Martian neighbor—is powered by a 5-
kilogram chunk of plutonium, acquired by NASA at great
expense.
*
F
o
r
m
o
r
e
o
n
t
h
i
s
,
s
e
e
“
F
e
d
E
x
B
a
n
d
w
i
d
t
h
”
i
n
Wh
a
t
If
?
*
S
e
e
c
h
a
p
t
e
r
7: H
o
w
t
o
M
o
v
e.
* For more on harnessing sources of power outdoors, see
chapter 16: How to Power Your House (on Earth).
* Although there are rumors Jupiter is considering setting up a
paywall.
*
A
l
t
h
o
u
g
h
i
f
y
o
u
r
e
a
l
l
y
w
a
n
t
t
o
,
a
b
s
o
l
u
t
e
l
y
,
g
o
f
o
r
i
t.
* The shape of a wheel that can roll smoothly on stairs was
derived by Dr. Anna Romanov and classmate David Allen
while they were mathematics students at Colorado State
University. Their design would work on stairs with a 45°
slope and step size; the exact shape of the petals could be
tweaked to fit a specific set of stairs.
* Tools like Google Earth and sky chart apps like Stellarium
and Sky Safari can help you plan out the shot.
* In theory, by the time this book is published, the James
Webb Space Telescope should have finally launched.
[Editor’s note: It was delayed again while this chapter was
being edited.]
* For those who weren’t around in the 1980s, lawn darts were
big heavy plastic darts with metal tips, similar to medieval
weapons, which were sold to children as part of a game that
involved throwing the darts high into the air. They were
eventually banned in the United States for reasons that seem
pretty obvious in retrospect.
* This is for a very accurate long drive. Accuracy for shorterrange chips may be higher.
* Quarterback Drew Brees, on the show Sport Science, threw
a football at an archery target 20 yards away, hitting the bullseye ten times out of ten. This suggests that under those
circumstances, his accuracy ratio is somewhere above 700—
better than a darts champion.
*
I
f
t
h
e
y
c
o
u
l
d
k
e
e
p
t
h
e
i
r
a
c
c
u
r
a
c
y
a
t
t
h
a
t
l
o
n
g
r
a
n
g
e
* If you expected the words “. . . when the Fire Nation
attacked!” here, you are of a very specific age.
* Vaccination continued in a few populations for a decade or
so after routine childhood vaccination ended, mainly among
people such as health care workers or soldiers who were
considered to be at higher risk of infection.
* I don’t know what year you’re reading this sentence; I hope
it’s still true.
*
“
O
r
g
a
n
i
c
”
m
e
a
n
s
“
c
a
r
b
o
n
-
b
a
s
e
d
,
”
a
f
t
e
r
a
l
l!
*
A
t
l
e
a
s
t
,
I
h
op
e
t
h
o
s
e
w
e
r
e
r
e
s
e
a
r
c
h
e
r
s.
* Burning of fossil fuels releases more carbon-12 and carbon13 into the atmosphere, which actually reduces the carbon-14,
but this effect is dwarfed by the huge increases caused by
nuclear testing.
* If people are showing up to vote for an exciting presidential
candidate, they might not be as familiar with the rest of the
candidates on the ballot as the more civically engaged people
who vote in a midterm.
*
O
r
i
s
i
t
“
B
o
b
s
C
a
s
e
y
”
?
* Catherine Knoll did end up being elected treasurer later, in
1988, and went on to also serve as lieutenant governor.
* Or perhaps they thought that the state treasurer, Bob Casey
#2, was running for governor midterm.
* He won with the help of campaign strategist James Carville,
who would later be part of Bill Clinton’s successful
presidential campaign.
* There are some exceptions to this. The US coast of the Gulf
of Mexico is thickly forested, despite lying in the desert
latitudes, thanks to the warm moist air from the Gulf. This is
also why the area has so many tornadoes.
* Another tree, dated by the late dendrochronologist Tom
Harlan, may be slightly older than Methuselah or Prometheus.
However, the tree’s record is disputed—the organization
Rocky Mountain Tree-Ring Research has been unable to
locate the core to verify the age.
* How do they measure a tree like that? You might think it
involves GPS or lasers or something, but no: researchers just
climb up and then dangle a tape measure down to the ground.
* Very fast sports cars accelerate at about 1 G, and need
specialized high-grip tires to do so.
* Your actual travel time will be a little more complicated to
work out, since at those speeds the curvature of the Earth
becomes significant. Your speed in the middle of your
journey would be fast enough that you’d lose contact with the
ground, and if you tried to hold on to a rail (or drove on the
ceiling), the centripetal acceleration would exceed your limits.
But the same curvature means that you’d be able to accelerate
a little harder near the beginning and end of your journey,
since the centrifugal force helps cancel out the effect of
gravity, giving you more leeway to accelerate forward while
staying under the 1.41 G limit.
* The Nobel Committee didn’t actually give him the prize for
the space-time stuff, in part because it was still considered
revolutionary and not fully tested. Luckily, he published four
papers in 1905, any one of which would probably be worthy
of a Nobel, so they gave it to him for one of the more
conventional ones.
* At least, it should be slowing down. Over the long term, the
Earth’s spin has been slowing steadily, but in recent decades
it’s actually sped up a little. Since about 1972—
coincidentally, when we started adding leap seconds—the
time it takes the Earth to complete one spin has gotten a few
milliseconds shorter. This is likely due to impossible-topredict turbulence in the currents in the Earth’s molten outer
core, but no one really knows for sure. It’s not too unusual—
the Earth has sped up and slowed down a number of times
over the last few centuries—and it’s unlikely to continue for
too much longer. But it’s still a little strange to think that the
Earth is speeding up and no one knows why.
* Editor’s note: If you would like to purchase all existing
copies of this book, please contact the Riverhead sales
department.
* In the 1990s, a panel of experts was assembled to ponder
the question of how to create markings that will make it clear
to future civilizations that they shouldn’t dig up our nuclear
waste, involving informational inscriptions in various
languages, diagrams, and ominous sculptures. The whole
exercise is a strange combination of gloom and optimism—
gloom that we’ve created something so dangerous that it
poses a threat not only to us, but to future civilizations—and
optimism that there will be future civilizations, long after
we’ve been forgotten, who might read and understand the
messages we leave for them.
*
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3: H
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*
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* If you asked me what the term crystalline basement meant
before I learned it, my guesses would include: “Mario Kart
level,
” “electronic music subgenre,
” “home improvement
project,
” and “illegal synthetic drug.”